Fix typos found by http://github.com/lyda/misspell-check

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157885 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/index.rst b/docs/index.rst
index ca31efa..53d3e7c 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -13,7 +13,7 @@
 research projects.
 
 Similarly, documentation is broken down into several high-level groupings
-targetted at different audiences:
+targeted at different audiences:
 
   * **Design & Overview**