Simplify Webpack's configuration

Using both include and test for a loader which is to process a single
file is more complex than necessary. Reduce that to a test only.

webpack.config.babel.js

         loaders: [ {
             // Version this build of the lib-jitsi-meet library.
 
-            include: `${__dirname}/JitsiMeetJS.js`,
             loader: 'string-replace',
             query: {
                 flags: 'g',
                             .trim(),
                 search: '{#COMMIT_HASH#}'
             },
-            test: /\.js$/
+            test: `${__dirname}/JitsiMeetJS.js`
         }, {
             // Transpile ES2015 (aka ES6) to ES5.