Replace godep with dep

vendor/github.com/spf13/pflag/.travis.yml

@@ -3,18 +3,19 @@ sudo: false
 language: go
 
 go:
-        - 1.6.3
-        - 1.7.3
-        - tip
+  - 1.7.3
+  - 1.8.1
+  - tip
 
 matrix:
-        allow_failures:
-                  - go: tip
+  allow_failures:
+    - go: tip
+
 install:
-        - go get github.com/golang/lint/golint
-        - export PATH=$GOPATH/bin:$PATH
-        - go install ./...
+  - go get github.com/golang/lint/golint
+  - export PATH=$GOPATH/bin:$PATH
+  - go install ./...
 
 script:
-        - verify/all.sh -v
-        - go test ./...
+  - verify/all.sh -v
+  - go test ./...