[lgtm] Add gmock libs to lgtm (#973)

Author: kcudnik

lgtm.yml

@@ -17,6 +17,8 @@ extraction:
       - libzmq3-dev
       - libzmq5
       - autoconf-archive
+      - libgtest-dev
+      - libgmock-dev
     after_prepare:
       - ls -l
       - git clone https://github.com/Azure/sonic-swss-common; pushd sonic-swss-common; ./autogen.sh; fakeroot dpkg-buildpackage -us -uc -b; popd