Make commaf only apply to go 1.6+
This is failing on 1.5 on travis. Fix the names to not be version
specific and update the version requirements.
diff --git a/comma_go15.go b/commaf.go
similarity index 97%
rename from comma_go15.go
rename to commaf.go
index 9d27cdc..620690d 100644
--- a/comma_go15.go
+++ b/commaf.go
@@ -1,4 +1,4 @@
-// +build go1.5
+// +build go1.6
package humanize
diff --git a/comma_go15_test.go b/commaf_test.go
similarity index 99%
rename from comma_go15_test.go
rename to commaf_test.go
index baf777b..21f7f9e 100644
--- a/comma_go15_test.go
+++ b/commaf_test.go
@@ -1,4 +1,4 @@
-// +build go1.5
+// +build go1.6
package humanize
