build(deps): remove babel-plugin-transform-es2015-modules-commonjs

Remove `babel-plugin-transform-es2015-modules-commonjs`, which is 6 years out-of-date and no longer supported. It generates security warnings in the console, because of outdated dependencies on `@babel/traverse`.

- transpile `.coffee` and `.cjsx` files from CJS to ESM with Babel.
- fix broken `module.exports` in a couple of places.
- `npm audit fix`.

app/pages/lab/field-guide/actions.js

@@ -155,4 +155,4 @@ var actions = {
   }
 };
 
-module.exports = actions;
+export default actions;

app/pages/project/stats/index.jsx

@@ -121,4 +121,4 @@ ProjectStatsPageController.propTypes = {
   params: PropTypes.object
 };
 
-module.exports = ProjectStatsPageController;
+export default ProjectStatsPageController;

babel.config.js

@@ -1,6 +1,7 @@
 module.exports = function (api) {
   api.cache(true);
   return {
+    sourceType: 'unambiguous',
     plugins: [
       [
         '@babel/plugin-transform-runtime',
@@ -14,34 +15,10 @@ module.exports = function (api) {
       ['@babel/preset-react', { runtime: 'automatic' }]
     ],
     env: {
-      development: {
-        plugins: [
-          [
-            'transform-es2015-modules-commonjs'
-          ]
-        ]
-      },
-      staging: {
-        plugins: [
-          [
-            'transform-es2015-modules-commonjs'
-          ]
-        ]
-      },
-      production: {
-        plugins: [
-          [
-            'transform-es2015-modules-commonjs'
-          ]
-        ]
-      },
       test: {
         plugins: [
           [
             'babel-plugin-rewire'
-          ],
-          [
-            'transform-es2015-modules-commonjs'
           ]
         ]
       }