Travis: Fail when changed files are detected (#1819)

This adds a new check to the Travis CI config which will cause the build to fail if any files change (This usually indicates that the committer forgot to rebuild Prism.). To implement this, we also add the `package-lock.json` file.

.travis.yml

@@ -9,9 +9,14 @@ branches:
   only:
   - gh-pages
   - /.*/
+before_install:
+- npm i -g npm@latest
+install:
+- npm ci
 before_script:
 - npm install -g gulp
 - gulp
+- gulp premerge
 script: npm test
 deploy:
   provider: npm

gulpfile.js

@@ -7,6 +7,7 @@ const concat = require('gulp-concat');
 const replace = require('gulp-replace');
 const pump = require('pump');
 const fs = require('fs');
+const simpleGit = require('simple-git');
 
 const paths = {
 	componentsFile: 'components.json',
@@ -202,7 +203,24 @@ function changelog(cb) {
 const components = minifyComponents;
 const plugins = series(languagePlugins, minifyPlugins);
 
+function gitChanges(cb) {
+	const git = simpleGit(__dirname);
+
+	git.status((err, res) => {
+		if (err) {
+			cb(new Error(`Something went wrong!\n${err}`));
+		} else if (res.files.length > 0) {
+			console.log(res);
+			cb(new Error('There are changes in the file system. Did you forget to run gulp?'));
+		} else {
+			cb();
+		}
+	});
+}
+
 
 exports.watch = watchComponentsAndPlugins;
 exports.default = parallel(components, plugins, componentsJsonToJs, build);
 exports.changelog = changelog;
+
+exports.premerge = gitChanges;