Int overflow on 32 bits arches

[eclipseo]

Golang 1.12.6 on i686 and armv7:

Testing    in: /builddir/build/BUILD/objecthash-d1e3d6079fc16f8f542183fb5b2fdc11d9f00866/_build/src
         PATH: /builddir/build/BUILD/objecthash-d1e3d6079fc16f8f542183fb5b2fdc11d9f00866/_build/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/sbin
       GOPATH: /builddir/build/BUILD/objecthash-d1e3d6079fc16f8f542183fb5b2fdc11d9f00866/_build:/usr/share/gocode
  GO111MODULE: off
      command: go test -buildmode pie -compiler gc -ldflags "-X github.com/benlaurie/objecthash/version=0 -X github.com/benlaurie/objecthash/version.commit=d1e3d6079fc16f8f542183fb5b2fdc11d9f00866 -extldflags '-Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld '"
      testing: github.com/benlaurie/objecthash
github.com/benlaurie/objecthash/go/objecthash
FAIL	github.com/benlaurie/objecthash/go/objecthash [build failed]BUILDSTDERR: # github.com/benlaurie/objecthash/go/objecthash [github.com/benlaurie/objecthash/go/objecthash.test]
BUILDSTDERR: ./objecthash_test.go:131:7: constant 9007199254740992 overflows int