Merge pull request #81 from obeattie/docs-fix

Small typo fix to extension docs
diff --git a/docs/extensions.rst b/docs/extensions.rst
index 357f592..3878d8c 100644
--- a/docs/extensions.rst
+++ b/docs/extensions.rst
@@ -219,7 +219,7 @@
 useful, another one would be fragment caching.
 
 When writing extensions you have to keep in mind that you are working with the
-Jinja2 template compiler which does not validate the node tree you are possing
+Jinja2 template compiler which does not validate the node tree you are passing
 to it.  If the AST is malformed you will get all kinds of compiler or runtime
 errors that are horrible to debug.  Always make sure you are using the nodes
 you create correctly.  The API documentation below shows which nodes exist and