fix "Op" service name case to "op" (#53)

Author: coder11

src/__test__/unit/builtInHandler.spec.ts

@@ -37,7 +37,7 @@ describe('Tests for default handler', () => {
         ({ fnName, args, retCode, result }) => {
             // arrange
             const req: CallServiceData = {
-                serviceId: 'Op',
+                serviceId: 'op',
                 fnName: fnName,
                 args: args,
                 tetraplets: [],

src/internal/defaultClientHandler.ts

@@ -18,7 +18,7 @@ const makeDefaultClientHandler = (): CallServiceHandler => {
         resp.result = errorMsg;
     };
     const mw: Middleware = (req: CallServiceData, resp: CallServiceResult, next: Function) => {
-        if (req.serviceId === 'Op') {
+        if (req.serviceId === 'op') {
             switch (req.fnName) {
                 case 'noop':
                     success(resp, {});