Fix typo in javadoc.

"mus" -> "must"

bug: https://code.google.com/p/android/issues/detail?id=178755
Change-Id: Ie418de27cc664597cc54f7c2a4395621bea0dc60
diff --git a/xml/src/main/java/org/xmlpull/v1/XmlPullParser.java b/xml/src/main/java/org/xmlpull/v1/XmlPullParser.java
index 0958bbf..bb3d130 100644
--- a/xml/src/main/java/org/xmlpull/v1/XmlPullParser.java
+++ b/xml/src/main/java/org/xmlpull/v1/XmlPullParser.java
@@ -916,7 +916,7 @@
      * Get next parsing event - element content will be coalesced and only one
      * TEXT event must be returned for whole element content
      * (comments and processing instructions will be ignored and entity references
-     * must be expanded or exception mus be thrown if entity reference can not be expanded).
+     * must be expanded or exception must be thrown if entity reference can not be expanded).
      * If element content is empty (content is "") then no TEXT event will be reported.
      *
      * <p><b>NOTE:</b> empty element (such as &lt;tag/>) will be reported