build: add tslint formatting task

Adds a Gulp task that fixes TSLint errors automatically when possible. This should make it easier to add/remove linting rules.

Author: crisbeto

tools/gulp/tasks/lint.ts

@@ -12,5 +12,10 @@ gulp.task('stylelint', execNodeTask(
   'stylelint', ['src/**/*.scss', '--config', 'stylelint-config.json', '--syntax', 'scss']
 ));
 
+const tsLintBaseFlags = ['-c', 'tslint.json', '+(src|e2e|tools)/**/*.ts'];
+
 /** Task to run TSLint against the e2e/ and src/ directories. */
-gulp.task('tslint', execNodeTask('tslint', ['-c', 'tslint.json', '+(src|e2e|tools)/**/*.ts']));
+gulp.task('tslint', execNodeTask('tslint', tsLintBaseFlags));
+
+/** Task that automatically fixes TSLint warnings. */
+gulp.task('tslint:fix', execNodeTask('tslint', [...tsLintBaseFlags, '--fix']));