Int overflow on 32 bits arches

[eclipseo]

Golang 1.12.6 on i686 and armv7:

Testing    in: /builddir/build/BUILD/goamz-2731d20f46f42449a49b3464271c5fba8da60ed6/_build/src
         PATH: /builddir/build/BUILD/goamz-2731d20f46f42449a49b3464271c5fba8da60ed6/_build/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/sbin
       GOPATH: /builddir/build/BUILD/goamz-2731d20f46f42449a49b3464271c5fba8da60ed6/_build:/usr/share/gocode
  GO111MODULE: off
      command: go test -buildmode pie -compiler gc -ldflags "-X github.com/AdRoll/goamz/version=0 -X github.com/AdRoll/goamz/version.commit=2731d20f46f42449a49b3464271c5fba8da60ed6 -extldflags '-Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld '"
      testing: github.com/AdRoll/goamz
github.com/AdRoll/goamz/autoscaling
PASS
ok  	github.com/AdRoll/goamz/autoscaling	0.015s
github.com/AdRoll/goamz/aws
OK: 12 passed
PASS
ok  	github.com/AdRoll/goamz/aws	0.516s
github.com/AdRoll/goamz/cloudfront
PASS
ok  	github.com/AdRoll/goamz/cloudfront	0.008s
github.com/AdRoll/goamz/dynamodb
OK: 17 passed, 42 skipped
PASS
ok  	github.com/AdRoll/goamz/dynamodb	0.012s
github.com/AdRoll/goamz/dynamodb/dynamizer
FAIL	github.com/AdRoll/goamz/dynamodb/dynamizer [build failed]
BUILDSTDERR: # github.com/AdRoll/goamz/dynamodb/dynamizer [github.com/AdRoll/goamz/dynamodb/dynamizer.test]
BUILDSTDERR: ./dynamizer_test.go:125:77: constant 18446744073709551615 overflows uint
BUILDSTDERR: ./dynamizer_test.go:143:77: constant 18446744073709551615 overflows uint