Update Dockerfile (#448)

Updated latest npm pg package, fixes https://github.com/toptal/haste-server/issues/378
- No I'll effects observed with latest release

Fixed typo in STORAGE_USERNAME environment variable 
- STORAGE_USENAME => STORAGE_USERNAME
- This resolved connection issues to postgres db (note the error message from the application logs did not make this immediately evident that it was an auth issue)

Dockerfile

@@ -11,7 +11,7 @@ COPY --chown=node:node . .
 
 RUN npm install && \
     npm install redis@0.8.1 && \
-    npm install pg@4.5.7 && \
+    npm install pg@8.11.3 && \
     npm install memcached@2.2.2 && \
     npm install aws-sdk@2.814.0 && \
     npm install rethinkdbdash@2.3.31
@@ -23,7 +23,7 @@ ENV STORAGE_TYPE=memcached \
     STORAGE_DB=2 \
     STORAGE_AWS_BUCKET= \
     STORAGE_AWS_REGION= \
-    STORAGE_USENAME= \
+    STORAGE_USERNAME= \
     STORAGE_PASSWORD= \
     STORAGE_FILEPATH=