sbt plugin file was added to ignore list among some other things.

Tyson · Tyson · commit 8e48a008100c · 2013-02-14T11:28:13.000-05:00
diff --git a/.gitignore b/.gitignore
@@ -1,4 +1,8 @@
 *.class
 target
 .idea/
-.idea_modules/
+.idea_modules/
+sbt/
+atlassian-ide-plugin.xml
+.history
+project/plugins.sbt
