change logrus package name to lowercase

[sadayuki-matsuno]

This errors occurred.

grouped write of manifest, lock and vendor: error while writing out vendor tree: error while exporting github.com/sirupsen/logrus: /var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/.gitignore already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/.travis.yml already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/CHANGELOG.md already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/LICENSE already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/README.md already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/alt_exit.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/alt_exit_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/doc.go already exists, no checkout
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/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/entry_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/examples/basic/basic.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/examples/hook/hook.go already exists, no checkout
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/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/formatter.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/formatter_bench_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hook_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks/syslog/README.md already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks/syslog/syslog.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks/syslog/syslog_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks/test/test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/hooks/test/test_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/json_formatter.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/json_formatter_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/logger.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/logger_bench_test.go already exists, no checkout
/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/logrus.go already exists, no checkout
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/var/folders/wc/20f2d7j91rq4cvf5rz27h68h0000gn/T/dep434114490/vendor/github.com/sirupsen/logrus/writer.go already exists, no checkout

Packages conflict with uppercase and lowercase, because logrus changed packagename to lowercase.
sirupsen/logrus#553

I want to update all vuls package's logrus package name to avoid this errors.
Target repositories are below.

1. kotakanbe/logrus-prefixed-formatter
2. kotakanbe/go-cve-dictionary
3. kotakanbe/goval-dictionary
4. future-architect/vuls