➕ add SourceMaps remapping support (close #22, close #25)

* Upgrade to istanbul-lib-instrument

* Pass intermediate source map to instrumenter

Pass the intermediate source map to the instrumenter that can be used
to remap the coverage report to the original source.
Requires istanbuljs-archived-repos/istanbul-lib-instrument#23.

Fixes #22, #7, karma-runner/karma-coverage#109,

index.js

@@ -17,5 +17,5 @@ module.exports = function(source, sourceMap) {
     var that = this;
     return instrumenter.instrument(source, this.resourcePath, function (error, source) {
         that.callback(error, source, instrumenter.lastSourceMap());
-    });
+    }, sourceMap);
 };