Added instalation of g++ to .yml

.gitlab-ci.yml

@@ -11,7 +11,7 @@ build_codes:
                         - build/
         before_script:
                 - 'apt-get -y update'
-                - 'apt-get -y install cmake'
+                - 'apt-get -y install cmake g++'
                 - 'apt-get -y upgrade'
 
         script: