Handle typescript in our linter. (#48)

## Summary:
We were only doing `.js` files before!

Issue: None

## Test plan:
I ran `ka-lint -v lib/utils.ts` in the Khan/our-lovely-cli repo,
and it said:
```
... LINTING
Beginning to lint 1 file(s)
--- Running Eslint:
```

Author: csilvers

Reviewers: MiguelCastillo

Required Reviewers:

Approved By: MiguelCastillo

Checks:

Pull Request URL: #48

runlint.py

@@ -414,6 +414,8 @@ def find_files_to_lint(files_and_directories,
                    '.js': 'javascript',
                    '.html': 'html',
                    '.jsx': 'javascript',
+                   '.ts': 'javascript',
+                   '.tsx': 'javascript',
                    '.less': 'less',
                    '.yaml': 'yaml',
                    '.yml': 'yaml',