Fix git pull origin master invocation in release instructions

Fix a small bug in the release instructions in that `git pull` doesn't
work and should be `git pull origin master` instead.

Author: brandur

docs/development.md

@@ -72,7 +72,7 @@ $ open coverage/index.html
 3. Build and push each gem, then tag the release and push that:
 
     ```shell
-    git pull
+    git pull origin master
 
     gem push riverqueue-${"${VERSION}"/v/}.gem
     pushd drivers/riverqueue-activerecord && gem push riverqueue-activerecord-${"${VERSION}"/v/}.gem && popd