fix suggested changes

Author: Polkaverse

src/librustc_error_codes/error_codes/E0703.md

@@ -1,18 +1,19 @@
-Invalid ABI(Application Binary Interface) used in the code.
+Invalid ABI (Application Binary Interface) used in the code.
 
 Erroneous code example:
 
 ```compile_fail,E0703
-extern "invalid" fn foo() {} //~ ERROR
+extern "invalid" fn foo() {} // error!
 
-fn main() { }
+# fn main() {}
 ```
+
 At present there the few predefined ABI's (like Rust, C, system, etc.)
 which we can use in our Rust code. Please verify the ABI from the
 given ABI. For example you can replace the given ABI from 'Rust'.
 
 ```
-extern "Rust" fn foo() {} //~ OK!
+extern "Rust" fn foo() {} // ok!
 
-fn main() { }
+# fn main() { }
 ```