Install Zip (#68)

This is for convenience so customers can package their actions inside of the runtime.
diff --git a/core/ruby2.5Action/Dockerfile b/core/ruby2.5Action/Dockerfile
index 0cfff5b..d9b249d 100644
--- a/core/ruby2.5Action/Dockerfile
+++ b/core/ruby2.5Action/Dockerfile
@@ -33,6 +33,7 @@
     apt-get -y update \
     # Upgrade installed packages to get latest security fixes if the base image does not contain them already.
     && apt-get upgrade -y --no-install-recommends \
+    && apt-get install -y zip \
     # Cleanup apt data, we do not need them later on.
     && rm -rf /var/lib/apt/lists/* \
     # create src directory to store action files
diff --git a/core/ruby2.6ActionLoop/Dockerfile b/core/ruby2.6ActionLoop/Dockerfile
index 4e30ade..42b01a5 100644
--- a/core/ruby2.6ActionLoop/Dockerfile
+++ b/core/ruby2.6ActionLoop/Dockerfile
@@ -42,6 +42,7 @@
     apt-get -y update \
     # Upgrade installed packages to get latest security fixes if the base image does not contain them already.
     && apt-get upgrade -y --no-install-recommends \
+    && apt-get install -y zip \
     # Cleanup apt data, we do not need them later on.
     && rm -rf /var/lib/apt/lists/* \
     # Create required directories