protobuf install fails on go1.11 on travis

[lantz]

The travis build seems to fail to run test-dependencies.sh when it tries to install protobuf as part of the gnxi installation:

7* Installing gnxi tools

274# google.golang.org/protobuf/proto

275../../../gopath/src/google.golang.org/protobuf/proto/proto_methods.go:18:23: cannot use m.ProtoMethods() (type *protoreflect.Message) as type *struct { pragma.NoUnkeyedLiterals; Flags uint64; Size func(struct { pragma.NoUnkeyedLiterals; Message protoreflect.Message; Flags uint8 }) struct { pragma.NoUnkeyedLiterals; Size int }; Marshal func(struct { pragma.NoUnkeyedLiterals; Message protoreflect.Message; Buf []byte; Flags uint8 }) (struct { pragma.NoUnkeyedLiterals; Buf []byte }, error); Unmarshal func(struct { pragma.NoUnkeyedLiterals; Message protoreflect.Message; Buf []byte; Flags uint8; Resolver interface { FindExtensionByName(protoreflect.FullName) (protoreflect.ExtensionType, error); FindExtensionByNumber(protoreflect.FullName, protowire.Number) (protoreflect.ExtensionType, error) } }) (struct { pragma.NoUnkeyedLiterals; Flags uint8 }, error); Merge func(struct { pragma.NoUnkeyedLiterals; Source protoreflect.Message; Destination protoreflect.Message }) struct { pragma.NoUnkeyedLiterals; Flags uint8 }; CheckInitialized func(struct { pragma.NoUnkeyedLiterals; Message protoreflect.Message }) (struct { pragma.NoUnkeyedLiterals }, error) } in return argument

276The command "./test-dependencies.sh" failed and exited with 2 during .
277
278Your build has been stopped.

Other people also seem to have run into issues installing protobuf on go1.11: https://github.com/golang/protobuf/issues/1094

This may also be related: https://github.com/golang/protobuf/issues/751