fiddling with travis build

Author: TiarkRompf

publish.sbt

@@ -40,15 +40,9 @@ pomExtra in Global := {
   </developers>
 }
 
-(for {
+credentials ++= (for {
   username <- Option(System.getenv().get("SONATYPE_USERNAME"))
   password <- Option(System.getenv().get("SONATYPE_PASSWORD"))
-} yield 
-  credentials += Credentials(
-                   "Sonatype Nexus Repository Manager", 
-                   "oss.sonatype.org", 
-                   username, 
-                   password)
-                 ).getOrElse(credentials ++= Seq())
+} yield Credentials("Sonatype Nexus Repository Manager", "oss.sonatype.org", username, password)).toSeq
 
 // NOTE: sonatypeRelease must be run explicitly, after `sbt release`