Use environment variables, rather than system properties

Author: retronym

Diff for: admin/publish-settings.sbt

@@ -1,7 +1,9 @@
-pgpPassphrase := Some(sys.props("PGP_PASSPHRASE").toArray)
+def env(key: String) = Option(System.getenv(key)).getOrElse("")
+
+pgpPassphrase := Some(env("PGP_PASSPHRASE").toArray)
 
 pgpPublicRing := file("admin/pubring.asc")
 
 pgpSecretRing := file("admin/secring.asc")
 
-credentials   += Credentials("Sonatype Nexus Repository Manager", "oss.sonatype.org", sys.props("SONA_USER"), sys.props("SONA_PASS"))
+credentials   += Credentials("Sonatype Nexus Repository Manager", "oss.sonatype.org", env("SONA_USER"), env("SONA_PASS"))