Fail CI on unlinted js code (#2178)

I noticed that #2131 was able to merge even though it contained a missing ;
which should have failed lint checks. I think the problem is that if fix is
enabled, running bin/web build fixes the issue and then the lint checks pass on
the fixed but uncommitted code.

We should avoid autofixing in environments that aren't development to avoid
merging unfixed code to master.

web/app/js/components/TapLink.jsx

@@ -35,6 +35,6 @@ TapLink.propTypes = {
 
 TapLink.defaultProps = {
   disabled: false
-}
+};
 
 export default TapLink;

web/app/webpack.config.js

@@ -38,7 +38,7 @@ module.exports = {
           {
             loader: 'eslint-loader',
             options: {
-              fix: true,
+              fix: process.env.NODE_ENV === 'development',
               emitWarning: process.env.NODE_ENV === 'development'
             }
           }