Use a fork of gometalinter

Until https://github.com/alecthomas/gometalinter/pull/289 is merged.
This reduces the runtime of the linter by 50x

Signed-off-by: Daniel Nephin <dnephin@docker.com>

dockerfiles/Dockerfile.lint

@@ -2,7 +2,7 @@ FROM    golang:1.8.3-alpine
 
 RUN     apk add -U git
 
-RUN     go get -u gopkg.in/alecthomas/gometalinter.v1 && \
+RUN     go get -u gopkg.in/dnephin/gometalinter.v1 && \
         mv /go/bin/gometalinter.v1 /usr/local/bin/gometalinter && \
         gometalinter --install
 

gometalinter.json

@@ -1,6 +1,6 @@
 {
   "Vendor": true,
-  "Deadline": "8m",
+  "Deadline": "2m",
   "Sort": ["linter", "severity", "path"],
   "Exclude": ["cli/compose/schema/bindata.go"],