Clean up E0747 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0747.md

@@ -1,4 +1,4 @@
-Generic arguments must be provided in the same order as the corresponding
+Generic arguments were not provided in the same order as the corresponding
 generic parameters are declared.
 
 Erroneous code example:
@@ -11,7 +11,7 @@ type X = S<(), 'static>; // error: the type argument is provided before the
 ```
 
 The argument order should be changed to match the parameter declaration
-order, as in the following.
+order, as in the following:
 
 ```
 struct S<'a, T>(&'a T);