fix typo

Closes: #326
Pull-request: https://github.com/sqlalchemy/mako/pull/326
Pull-request-sha: a04258282a896237596e926135f0d179686e64ac

Change-Id: I54896fdaeb4a5b7f8f2d1d13afeaa66377bc6ab5

mako/parsetree.py

diff --git a/mako/parsetree.py b/mako/parsetree.py
index c1629d9..5cef120 100644
--- a/mako/parsetree.py
+++ b/mako/parsetree.py
@@ -344,7 +344,7 @@
             elif key in nonexpressions:
                 if re.search(r"\${.+?}", self.attributes[key]):
                     raise exceptions.CompileException(
-                        "Attibute '%s' in tag '%s' does not allow embedded "
+                        "Attribute '%s' in tag '%s' does not allow embedded "
                         "expressions" % (key, self.keyword),
                         **self.exception_kwargs,
                     )