Merge pull request #3722 from matrix-org/travis/babel7

[BREAKING] Refactor the entire build process for babel@7 and TypeScript (chunk 1 of many)

.babelrc

@@ -5,8 +5,7 @@
             "targets": {
                 "browsers": [
                     "last 2 versions"
-                ],
-                "node": 12
+                ]
             },
             "modules": "commonjs"
         }],

src/MatrixClientPeg.js

@@ -247,5 +247,10 @@ class _MatrixClientPeg {
 if (!global.mxMatrixClientPeg) {
     global.mxMatrixClientPeg = new _MatrixClientPeg();
 }
+
+// We export both because the syntax is slightly different with
+// our babel changes. We maintain both for backwards compatibility
+// and for babel to be happy.
+// TODO: Convert this to a single export
 export default global.mxMatrixClientPeg;
 export const MatrixClientPeg = global.mxMatrixClientPeg;