Use pep8 version of method set_name (#508)

* Fix one occurrence of setName that was not converted to the
  pep8-compliant names.

pyparsing/common.py

@@ -206,7 +206,7 @@ class pyparsing_common:
     scientific notation and returns a float"""
 
     # streamlining this expression makes the docs nicer-looking
-    number = (sci_real | real | signed_integer).setName("number").streamline()
+    number = (sci_real | real | signed_integer).set_name("number").streamline()
     """any numeric expression, returns the corresponding Python type"""
 
     fnumber = (