Merge #78: Travis: enable goimports static analyzer as critical.

9496034 Travis: disable gofmt linter. (JeremyRand)
99cb7d9 Travis: enable goimports static analyzer as critical. (JeremyRand)

Pull request description:

  Depends on #54 and #77 .  Should be mergeable after those are merged, assuming Travis passes at that point.

Tree-SHA512: 174fc0d5b0bd5734703d4e97d04d70389883071fec41436ef6a93b543e449032db8faab2ab0a3b287a3c180504e3a2e64d446c613cc4643016c90e13a4744c7a

.travis/script

@@ -17,6 +17,7 @@ gometalinter.v2 --install
 # maligned is disabled because of these comments:
 # * https://www.reddit.com/r/golang/comments/3lahav/aligncheck_helps_to_find_inefficiently_packed/cv4u4lg/
 # * https://www.reddit.com/r/golang/comments/3lahav/aligncheck_helps_to_find_inefficiently_packed/cv5wnom/
+# gofmt is disabled because it's a subset of goimports.
 # test is disabled because we already do tests earlier in the script.
 # The --exclude line disables warnings on the portion of x509 that is copied
 # verbatim from the Go standard library.
@@ -29,7 +30,7 @@ gometalinter.v2 --enable-all \
 --disable=gas \
 --disable=gochecknoglobals \
 --disable=gocyclo \
---disable=goimports \
+--disable=gofmt \
 --disable=golint \
 --disable=ineffassign \
 --disable=lll \
@@ -51,6 +52,7 @@ echo ""
 echo "gometalinter non-critical (warnings expected):"
 gometalinter.v2 --enable-all \
 --disable=maligned \
+--disable=gofmt \
 --disable=test \
 --concurrency=3 \
 --deadline=10m \