Explicitly add nss to the build image

It appears that nss has been removed from current versions
for Apline Linux [1]. It needs to be there for secure
connections.

[1] docker-library/openjdk#289

.gitlab-ci.yml

@@ -11,6 +11,7 @@ variables:
   ANDROID_SDK_TOOLS:   "4333796"
 
 before_script:
+  - apk add --no-cache nss
   - apk add --update python git gzip tar openjdk8 bash wget unzip libstdc++ 
   - wget --quiet --output-document=android-sdk.zip https://dl.google.com/android/repository/sdk-tools-linux-${ANDROID_SDK_TOOLS}.zip
   - unzip -d android-sdk-linux android-sdk.zip