Fix a typo.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112092 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Basic/SourceManager.h b/include/clang/Basic/SourceManager.h
index 91ade22..dbd7d52 100644
--- a/include/clang/Basic/SourceManager.h
+++ b/include/clang/Basic/SourceManager.h
@@ -50,7 +50,7 @@
     C_User, C_System, C_ExternCSystem
   };
 
-  /// ContentCache - Once instance of this struct is kept for every file
+  /// ContentCache - One instance of this struct is kept for every file
   /// loaded or used.  This object owns the MemoryBuffer object.
   class ContentCache {
     enum CCFlags {