Fix indent in E0591.md

Author: reddevilmidzy

compiler/rustc_error_codes/src/error_codes/E0591.md

@@ -62,14 +62,14 @@ This pattern should be rewritten. There are a few possible ways to do this:
  and do the cast in the fn body (the preferred option)
 - cast the fn item of a fn pointer before calling transmute, as shown here:
 
- ```
- # extern "C" fn foo(_: Box<i32>) {}
- # use std::mem::transmute;
- # unsafe {
- let f: extern "C" fn(*mut i32) = transmute(foo as extern "C" fn(_));
- let f: extern "C" fn(*mut i32) = transmute(foo as usize); // works too
- # }
- ```
+```
+# extern "C" fn foo(_: Box<i32>) {}
+# use std::mem::transmute;
+# unsafe {
+let f: extern "C" fn(*mut i32) = transmute(foo as extern "C" fn(_));
+let f: extern "C" fn(*mut i32) = transmute(foo as usize); // works too
+# }
+```
 
 The same applies to transmutes to `*mut fn()`, which were observed in practice.
 Note though that use of this type is generally incorrect.

tests/ui/explain/basic.stdout

@@ -56,10 +56,10 @@ This pattern should be rewritten. There are a few possible ways to do this:
  and do the cast in the fn body (the preferred option)
 - cast the fn item of a fn pointer before calling transmute, as shown here:
 
- ```
- let f: extern "C" fn(*mut i32) = transmute(foo as extern "C" fn(_));
- let f: extern "C" fn(*mut i32) = transmute(foo as usize); // works too
- ```
+```
+let f: extern "C" fn(*mut i32) = transmute(foo as extern "C" fn(_));
+let f: extern "C" fn(*mut i32) = transmute(foo as usize); // works too
+```
 
 The same applies to transmutes to `*mut fn()`, which were observed in practice.
 Note though that use of this type is generally incorrect.