[BUGFIX release] Remove sourceMappingURL for dag-map.

Babel is not properly ingesting the sourcemaps (even when the upstream
funnel brings the mapping file in with it), this commit strips it out to
avoid errors during uglification (reported in
ember-cli/ember-cli-terser#29).

broccoli/packages.js

@@ -121,10 +121,19 @@ module.exports.backburnerES = function _backburnerES() {
 }
 
 module.exports.dagES = function _dagES() {
-  return funnelLib('dag-map', {
+  let lib = funnelLib('dag-map', {
     files: ['dag-map.js'],
     annotation: 'dag-map es'
   });
+
+  return new StringReplace(lib, {
+    files: ['dag-map.js'],
+    patterns: [{
+      match: /\/\/# sourceMappingURL=dag-map.js.map/g,
+      replacement: ''
+    }],
+    annotation: 'remove sourcemap annotation (dag-map)'
+  });
 }
 
 module.exports.routeRecognizerES = function _routeRecognizerES() {