Require go v1.5 for compilation

Google cloud package requires go v1.5 to compile, so we need to require the same for rclone.

Fixes #408

.travis.yml

@@ -7,16 +7,15 @@ os:
 # - osx
 
 go:
-  - 1.4.2
   - 1.5.3
   - 1.6
   - tip
 
 install:
  - go get -t ./...
- - '[[ `go version` =~ go1.[0-4][^0-9] ]] || go get -u github.com/kisielk/errcheck'
+ - go get -u github.com/kisielk/errcheck
  - go get -u golang.org/x/tools/cmd/goimports
- - '[[ `go version` =~ go1.[0-4][^0-9] ]] || go get -u github.com/golang/lint/golint'
+ - go get -u github.com/golang/lint/golint
 
 script:
   - make check