fix spelling

NEWS.rst

@@ -38,7 +38,7 @@ Latest
 * Minor: Updated waf to 2.0.10.
 * Patch: Hide the output of the mklink command on Windows when calling the
   create_symlink function (the output is logged when an error occurs)
-* Minor: Allow persistant virtualenv
+* Minor: Allow persistent virtualenv
 * Minor: Added capability to prevent git dependencies from pulling submodules.
 * Minor: Added Context dependency_node() function to return a waf node to a
   dependency. Making it easy to use Waf's ant_glob(...) function.