Update .gitlab-ci.yml file

.gitlab-ci.yml

@@ -5,6 +5,7 @@ stages:          # List of stages for jobs, and their order of execution
 ############ YAML ANCHORS ############
 .script_gcc5_template: &script_gcc5_definition
   - apt-get update
+  - apt-get install software-properties-common
   - add-apt-repository ppa:ubuntu-toolchain-r/test
   - apt-get update
   - apt-get install gcc-snapshot