fix(getLocalIdent): add rootContext support (webpack >= v4.0.0) (#681)

Author: yavorsky

lib/getLocalIdent.js

@@ -6,8 +6,15 @@ var loaderUtils = require("loader-utils");
 var path = require("path");
 
 module.exports = function getLocalIdent(loaderContext, localIdentName, localName, options) {
-	if(!options.context)
-		options.context = loaderContext.options && typeof loaderContext.options.context === "string" ? loaderContext.options.context : loaderContext.context;
+	if(!options.context) {
+		if (loaderContext.rootContext) {
+			options.context = loaderContext.rootContext;
+		} else if (loaderContext.options && typeof loaderContext.options.context === "string") {
+			options.context = loaderContext.options.context;
+		} else {
+			options.context = loaderContext.context;
+		}
+	}
 	var request = path.relative(options.context, loaderContext.resourcePath);
 	options.content = options.hashPrefix + request + "+" + localName;
 	localIdentName = localIdentName.replace(/\[local\]/gi, localName);