hot fix

parentheses error

Author: onlyjus

docx/oxml/text.py

@@ -299,7 +299,7 @@ def add_underline(self, style):
         """
         Return a newly added <w:u w:val=style/> child element.
         """
-        u = CT_String.new('w:u', WD_UNDERLINE.stringDict[style]))
+        u = CT_String.new('w:u', WD_UNDERLINE.stringDict[style])
         self.insert(0, u)
         return u