fix(server): fix error message on bad implementation

Author: knagaitsev

lib/utils/getSocketServerImplementation.js

@@ -29,7 +29,7 @@ function getSocketServerImplementation(options) {
 
   if (!serverImplFound) {
     throw new Error(
-      "serverMode must be a string denoting a default implementation (eg. 'sockjs'), a full path to " +
+      "serverMode must be a string denoting a default implementation (e.g. 'sockjs'), a full path to " +
         'a JS file which exports a class extending BaseServer (webpack-dev-server/lib/servers/BaseServer) ' +
         'via require.resolve(...), or the class itself which extends BaseServer'
     );