Install tools before flipping module mode on

This is to work around golang/go#24250.

.travis.yml

@@ -3,7 +3,6 @@ go:
  - stable
 go_import_path: github.com/harmony-one/harmony
 install:
- - env GO111MODULE=on
  - export GOPATH=$HOME/gopath
  - export CGO_CPPFLAGS="-I$GOPATH/src/github.com/harmony-one/bls/include -I$GOPATH/src/github.com/harmony-one/mcl/include"
  - export CGO_LDFLAGS="-L$GOPATH/src/github.com/harmony-one/bls/lib -L$GOPATH/src/github.com/harmony-one/mcl/lib"
@@ -19,14 +18,15 @@ install:
  - cd bls
  - make
  - cd ../harmony
- - go get -t -v ./...
  - go get -u golang.org/x/lint/golint
  - go get -u golang.org/x/tools/cmd/goimports
- - go get gopkg.in/check.v1
  - go get github.com/harmony-ek/gencodec
  - go get github.com/golang/mock/gomock
  - go get github.com/golang/protobuf/protoc-gen-go
  - ./scripts/install_protoc.sh -V 3.6.1
+ - env GO111MODULE=on
+ - go get -t -v ./...
+ - go get gopkg.in/check.v1
  - ./scripts/travis_checker.sh
  - go build -v ./...
 script: