Don't include user and hostname into build and build verbose.

Index: .promu.yml
--- .promu.yml.orig
+++ .promu.yml
@@ -16,12 +16,12 @@ build:
             - builtinassets
         windows:
             - builtinassets
-    flags: -a
+    flags: -v -a
     ldflags: |
         -X github.com/prometheus/common/version.Version={{.Version}}
         -X github.com/prometheus/common/version.Revision={{.Revision}}
         -X github.com/prometheus/common/version.Branch={{.Branch}}
-        -X github.com/prometheus/common/version.BuildUser={{user}}@{{host}}
+        -X github.com/prometheus/common/version.BuildUser=OpenBSD
         -X github.com/prometheus/common/version.BuildDate={{date "20060102-15:04:05"}}
 tarball:
     # Whenever there are new files to include in the tarball,