chore(.travis.yml): use cask exec emacs to build js/input-method.js

.travis.yml

@@ -74,7 +74,7 @@ script:
   - lean --server < js/completion_input.in | grep "|" | grep -v "^private\." | sort | uniq | sed -e "s/\([^|]\+\)|\(.\+\)/{name:\"\1\", value:\"\1\", meta:\"\2\"},/" >> js/completion.js
   - echo "]" >> js/completion.js
   # Build input-method.js
-  - emacs --no-site-file --no-site-lisp -q --batch -l ./elisp/org-html-export.el -l ./lean/src/emacs/lean-input.el -f lean-input-export-translations-to-stdout > js/input-method.js
+  - cask exec emacs --no-site-file --no-site-lisp -q --batch -l ./elisp/org-html-export.el -l ./lean/src/emacs/lean-input.el -f lean-input-export-translations-to-stdout > js/input-method.js
   # Push to gh-pages
   - if [[ "${REPO}" == "BLESSED" ]] && [[ "${TRAVIS_PULL_REQUEST}" == "false" ]] ; then
       git config --global user.email "notifications@travis-ci.org" &&