Use one RUN to optimize layering

Since each RUN creates its own layer that needs to be downloaded and layered
to create the image, combining the cleanup steps into the same RUN shrinks the
image size quite a bit.

Before:      84MB
After:       75.2MB

swagger-ui/Dockerfile

@@ -15,11 +15,12 @@ ENV PORT 80
 
 WORKDIR /app
 
-RUN apk add --no-cache openssl
-RUN wget -qO- https://github.com/swagger-api/swagger-ui/archive/$VERSION.tar.gz | tar xvz
-RUN cp -r $FOLDER/dist/* . && rm -rf $FOLDER
-RUN npm install -g http-server
-RUN apk del openssl
+RUN apk add --no-cache openssl \
+  && wget -qO- https://github.com/swagger-api/swagger-ui/archive/$VERSION.tar.gz | tar xvz \
+  && cp -r $FOLDER/dist/* . \
+  && rm -rf $FOLDER \
+  && npm install -g http-server \
+  && apk del openssl
 
 ADD run.sh run.sh