fix: pass proper context param to runtime generator

BREAKING CHANGE:
Possible breaks third-party runtime generators. Earlier `context` param was containing _path to compilation root context_, e.g. folder where webpack compilation occurs. This is wrong behaviour, because meaning of this param is a _folder where svg image is located_. So it was changed in this commit.
If your custom runtime generator breaks after this update use `loaderContext.rootContext` option instead of `context`.

Closes: #186

Author: kisenka

lib/loader.js

@@ -16,7 +16,7 @@ module.exports = function loader(content) {
 
   const done = this.async();
   const loaderContext = this;
-  const { resourcePath, rootContext, loaderIndex } = loaderContext;
+  const { resourcePath, loaderIndex } = loaderContext;
   // webpack 1 compat
   const resourceQuery = loaderContext.resourceQuery || '';
   const compiler = loaderContext._compiler;
@@ -74,7 +74,7 @@ module.exports = function loader(content) {
   }
   svgCompiler.addSymbol({ id, content, path: resourcePath + resourceQuery })
     .then((symbol) => {
-      const runtime = runtimeGenerator({ symbol, config, context: rootContext, loaderContext });
+      const runtime = runtimeGenerator({ symbol, config, context: loaderContext.context, loaderContext });
       done(null, runtime);
     }).catch(done);
 };