Fix a typo in the PCH internals documentation

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164409 91177308-0d34-0410-b5e6-96231b3b80d8

docs/PCHInternals.html

@@ -631,7 +631,7 @@ the model:
   find both declarations, but the AST nodes are unrelated. This would
   result in a compilation error, due to an ambiguity in name
   lookup. Therefore, the AST reader performs declaration merging
-  according to the appropriate langauge semantics, ensuring that the
+  according to the appropriate language semantics, ensuring that the
   two disjoint declarations are merged into a single redeclaration
   chain (with a common canonical declaration), so that it is as if one
   of the headers had been included before the other.</dd>