Update base.py

adding unzip to base packages so you can just run unzip on the terminal (closing https://github.com/jupyter/repo2docker/issues/251)

repo2docker/buildpacks/base.py

@@ -170,6 +170,8 @@ class BuildPack:
             # FIXME: Use npm from nodesource!
             # Everything seems to depend on npm these days, unfortunately.
             "npm",
+            
+            "unzip",
         }
 
     def get_env(self):