Fix gitlab-ci gtk dependancies.

.gitlab-ci.yml

@@ -1,8 +1,9 @@
 # Optional: Install a C compiler, cmake and git into the container.
 # You will often need this when you (or any of your dependencies) depends on C code.
-# before_script:
-# - apt-get update -yqq
-# - apt-get install -yqq --no-install-recommends build-essential
+before_script:
+- apt-get update -yqq
+- apt-get install -yqq --no-install-recommends build-essential
+- apt-get install -y libgtk-3-dev
 
 # kcov
 # - apt-get install -y libcurl4-openssl-dev libelf-dev libdw-dev cmake gcc binutils-dev libiberty-dev