E0577 fixed Sea struct CamelCase/sea module snake_case

Author: CorinJG

compiler/rustc_error_codes/src/error_codes/E0577.md

@@ -3,14 +3,14 @@ Something other than a module was found in visibility scope.
 Erroneous code example:
 
 ```compile_fail,E0577,edition2018
-pub struct sea;
+pub struct Sea;
 
-pub (in crate::sea) struct Shark; // error!
+pub (in crate::Sea) struct Shark; // error!
 
 fn main() {}
 ```
 
-`sea` is not a module, therefore it is invalid to use it in a visibility path.
+`Sea` is not a module, therefore it is invalid to use it in a visibility path.
 To fix this error we need to ensure `sea` is a module.
 
 Please note that the visibility scope can only be applied on ancestors!