fix(e2e): without devTools

according to electron-userland/spectron#174 (comment) this might help re error like in https://travis-ci.org/artemv/angular-electron-spectron/builds/500315009

..but this also could be node version dependent as I don't have it locally on MacOS & Node 9

Author: artemv

Diff for: e2e/main.spec.ts

@@ -22,7 +22,7 @@ describe('angular-electron App', function () {
 
   it('creates initial windows', async function () {
     const count = await client.getWindowCount();
-    expect(count).to.equal(2);
+    expect(count).to.equal(1);
   });
 
 });

Diff for: main.ts

@@ -32,7 +32,9 @@ function createWindow() {
     }));
   }
 
-  win.webContents.openDevTools();
+  if (serve) {
+    win.webContents.openDevTools();
+  }
 
   // Emitted when the window is closed.
   win.on('closed', () => {