Cleanup from nodejs#623

Ran the script and noticed a few issues:
* Removed whitespace from Dockerfile-stretch.template to match the
  existing files
* Let the script update the other files for consistency

Author: kfarnung

6/Dockerfile

@@ -51,7 +51,6 @@ RUN set -ex \
     gpg --keyserver hkp://keyserver.pgp.com:80 --recv-keys "$key" || \
     gpg --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
     gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" ; \
-
   done \
   && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
   && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz.asc" \

8/slim/Dockerfile

@@ -17,7 +17,8 @@ RUN set -ex \
   ; do \
     gpg --keyserver hkp://pgp.mit.edu:80 --recv-keys "$key" || \
     gpg --keyserver hkp://keyserver.pgp.com:80 --recv-keys "$key" || \
-    gpg --keyserver hkp://ha.pool.sks-keyservers.net:80 --recv-keys "$key" ; \
+    gpg --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
+    gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" ; \
   done
 
 ENV NODE_VERSION 8.9.4

Dockerfile-stretch.template

@@ -51,8 +51,6 @@ RUN set -ex \
     gpg --keyserver hkp://keyserver.pgp.com:80 --recv-keys "$key" || \
     gpg --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
     gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" ; \
-
-
   done \
   && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
   && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz.asc" \