Tiny typo fix

core/src/main/scala/org/apache/spark/Logging.scala

@@ -112,7 +112,7 @@ trait Logging {
     }
     Logging.initialized = true
 
-    // Force a call into slf4j to initialize it avoids this happening from mutliple threads
+    // Force a call into slf4j to initialize it. Avoids this happening from mutliple threads
     // and triggering this: http://mailman.qos.ch/pipermail/slf4j-dev/2010-April/002956.html
     log
   }
@@ -121,4 +121,4 @@ trait Logging {
 object Logging {
   @volatile private var initialized = false
   val initLock = new Object()
-}
\ No newline at end of file
+}