Merge pull request #266 from jitsi/tmp_ss_fix

fix(SS): Temp fix for SS when the extension is not ready after 500ms after the install

modules/RTC/ScreenObtainer.js

                         window.setTimeout(function () {
                             doGetStreamFromExtension(self.options,
                                 streamCallback, failCallback);
-                        }, 500);
+                        }, 2000);
                     },
                     this.handleExtensionInstallationError.bind(this,
                         options, streamCallback, failCallback)