Can't compile rest activity

[fcastill]

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Current behavior (how does the issue manifest):
When building an app using the rest activity it fails with:

# app/vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:38: invalid identifier character U+201C '“'
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:38: undefined: “Content
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:49: undefined: Type”
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:53: invalid identifier character U+201D '”'
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:59: invalid identifier character U+201C '“'
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:59: undefined: “application
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:74: undefined: json”
vendor/github.com/TIBCOSoftware/flogo-contrib/activity/rest/activity.go:174:78: invalid identifier character U+201D '”'
FATAL: command "build" failed: exit status 2

Expected behavior:
Building an app with a rest activity should complete successfully.

Please tell us about your environment (Operating system, docker version, browser & verison if webui, etc): MacOS 10.14

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): Latest