Clean up E0130 error explanation

src/librustc_error_codes/error_codes/E0130.md

-You declared a pattern as an argument in a foreign function declaration.
+A pattern was declared as an argument in a foreign function declaration.
 
 Erroneous code example:
 
@@ -9,7 +9,7 @@ extern {
 }
 ```
 
-Please replace the pattern argument with a regular one. Example:
+To fix this error, replace the pattern argument with a regular one. Example:
 
 ```
 struct SomeStruct {