fix typo and unit test

Author: lolbinarycat

src/librustdoc/lib.rs

@@ -656,7 +656,7 @@ fn opts() -> Vec<RustcOptGroup> {
             FlagMulti,
             "",
             "disable-minification",
-            "diable the minification of CSS/JS files (perma-unstable, do not use with cached files)",
+            "disable the minification of CSS/JS files (perma-unstable, do not use with cached files)",
             "",
         ),
         // deprecated / removed options

tests/run-make/rustdoc-default-output/output-default.stdout

@@ -194,7 +194,8 @@ Options:
         --doctest-compilation-args add arguments to be used when compiling doctests
 
         --disable-minification 
-                        diable the minification of CSS/JS files
+                        disable the minification of CSS/JS files
+                        (perma-unstable, do not use with cached files)
         --plugin-path DIR
                         removed, see issue #44136
                         <https://github.com/rust-lang/rust/issues/44136> for