Merge pull request scala#84 from SethTisue/sbt-0.13.15

SethTisue · web-flow · commit e90b6795a68d · 2017-04-10T19:12:25.000-05:00
upgrade sbt to 0.13.15 (from 0.13.13)
diff --git a/project/build.properties b/project/build.properties
@@ -1 +1 @@
-sbt.version=0.13.13
+sbt.version=0.13.15
