Add 32-bit testing to CI (#920)

Run Go tests with 32-bit to validate value overflow.

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

Diff for: .circleci/config.yml

@@ -16,6 +16,7 @@ jobs:
 
     steps:
     - prometheus/setup_environment
+    - run: GOHOSTARCH=386 GOARCH=386 make test
     - run: make
     - prometheus/store_artifact:
         file: postgres_exporter