Address linting issues #52

cmd/generate/golang/golang.go:29:22: Error return value of `Cmd.MarkFlagRequired` is not checked (errcheck)
        Cmd.MarkFlagRequired(flagkeys.GoPackageName)
                            ^
cmd/generate/golang/golang.go:30:17: Error return value of `viper.BindPFlag` is not checked (errcheck)
        viper.BindPFlag(flagkeys.GoPackageName, Cmd.Flags().Lookup(flagkeys.GoPackageName))
                       ^
cmd/generate/generate.go:26:33: Error return value of `Root.MarkPersistentFlagRequired` is not checked (errcheck)
        Root.MarkPersistentFlagRequired(flagkeys.FlagManifestPath)
                                       ^
cmd/generate/generate.go:27:17: Error return value of `viper.BindPFlag` is not checked (errcheck)
        viper.BindPFlag(flagkeys.FlagManifestPath, Root.PersistentFlags().Lookup(flagkeys.FlagManifestPath))
                       ^
cmd/generate/generate.go:29:17: Error return value of `viper.BindPFlag` is not checked (errcheck)
        viper.BindPFlag(flagkeys.OutputPath, Root.PersistentFlags().Lookup(flagkeys.OutputPath))
                       ^
cmd/generate/generate.go:30:33: Error return value of `Root.MarkPersistentFlagRequired` is not checked (errcheck)
        Root.MarkPersistentFlagRequired(flagkeys.OutputPath)
                                       ^
cmd/generate/generate_test.go:37:14: Error return value of `Root.Execute` is not checked (errcheck)
        Root.Execute()
                    ^
cmd/generate/generate_test.go:62:14: Error return value of `Root.Execute` is not checked (errcheck)
        Root.Execute()
                    ^