Minor change

Author: Ayush Kumar Mishra

src/librustc_error_codes/error_codes/E0628.md

@@ -16,7 +16,7 @@ fn main() {
 
 At present, it is not permitted to pass more than one explicit
 parameter for a generator.This can be fixed by using
-at most one parameter for the generator. For example, we might resolve
+at most 1 parameter for the generator. For example, we might resolve
 the previous example by passing only one parameter.
 
 ```