DOC: a if statement -> an if statement (#119)

Author: star1327p

.pylintrc

@@ -458,7 +458,7 @@ max-args=10
 # Maximum number of attributes for a class (see R0902).
 max-attributes=10
 
-# Maximum number of boolean expressions in a if statement
+# Maximum number of boolean expressions in an if statement
 max-bool-expr=5
 
 # Maximum number of branch for function / method body