Move new-from-rev to step run

This change moves the specification of the diff to check against to
the invocation of the command, allowing local runs to run against the
entire project.

Thanks @benwh.

.circleci/config.yml

@@ -51,7 +51,7 @@ jobs:
       - run:
           name: Lint
           command: |
-            ${GOPATH}/bin/golangci-lint run
+            ${GOPATH}/bin/golangci-lint run --new-from-rev=origin/master
 
   build:
     <<: *docker_golang

.golangci.yml

@@ -202,6 +202,3 @@ issues:
   # of integration: much better don't allow issues in new code.
   # Default is false.
   new: false
-
-  # Show only new issues created after git revision `origin/master`
-  new-from-rev: origin/master