Fixed typos in documentation

--HG--
branch : trunk
diff --git a/jinja2/tests.py b/jinja2/tests.py
index 01246ff..37e6f31 100644
--- a/jinja2/tests.py
+++ b/jinja2/tests.py
@@ -22,7 +22,7 @@
 
 
 def test_even(value):
-    """Return true of the variable is even."""
+    """Return true if the variable is even."""
     return value % 2 == 0