fic: copy directory after installing zip (#444)

This should allow the `.ci/build` script to cache the `zip` installation layer between builds hopefully improving the build times slightly when starting fresh 😄

Author: masterful

.ci/Dockerfile

@@ -1,13 +1,13 @@
 FROM node:12
 
-WORKDIR /lambda
-
-COPY . /lambda
-
 RUN apt-get update \
     && apt-get install -y zip \
     && rm -rf /var/lib/apt/lists/*
 
+WORKDIR /lambda
+
+COPY . /lambda
+
 RUN yarn install \
     && yarn run dist