Fix test-tidy self test

Install rustup on first Travis job.
Only use rustfmt::skip as an outer attribute.

.travis.yml

@@ -4,6 +4,9 @@ matrix:
   fast_finish: true
   include:
     - sudo: false
+      before_install:
+        - curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain none -y
+        - source ~/.profile
       script:
          - ./mach test-tidy --no-progress --all
          - ./mach test-tidy --no-progress --self-test

python/tidy/servo_tidy_tests/test_tidy.py

@@ -105,14 +105,8 @@ class CheckTidiness(unittest.TestCase):
     def test_rust(self):
         errors = tidy.collect_errors_for_files(iterFile('rust_tidy.rs'), [], [tidy.check_rust], print_text=False)
         self.assertEqual('extra space after use', errors.next()[2])
-        self.assertEqual('extra space after {', errors.next()[2])
-        self.assertEqual('extra space before }', errors.next()[2])
-        self.assertEqual('use statement spans multiple lines', errors.next()[2])
         self.assertEqual('missing space before }', errors.next()[2])
-        self.assertTrue('use statement is not in alphabetical order' in errors.next()[2])
         self.assertEqual('use statement contains braces for single import', errors.next()[2])
-        self.assertTrue('use statement is not in alphabetical order' in errors.next()[2])
-        self.assertEqual('encountered whitespace following a use statement', errors.next()[2])
         self.assertTrue('mod declaration is not in alphabetical order' in errors.next()[2])
         self.assertEqual('mod declaration spans multiple lines', errors.next()[2])
         self.assertTrue('extern crate declaration is not in alphabetical order' in errors.next()[2])

tests/unit/malloc_size_of/lib.rs

@@ -1,7 +1,6 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-#![rustfmt::skip]
 
 /**
 ```
@@ -21,6 +20,7 @@ fn main() {
 */
 pub fn imports_ok() {}
 
+#[rustfmt::skip]
 pub mod does_not_impl_malloc_size_of {
     /**
     ```compile_fail,E0277
@@ -63,6 +63,7 @@ pub mod does_not_impl_malloc_size_of {
     pub fn rc() {}
 }
 
+#[rustfmt::skip]
 pub mod does_not_impl_malloc_shallow_size_of {
     /**
     ```compile_fail,E0277

tests/unit/script_plugins/lib.rs

@@ -1,8 +1,8 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-#![rustfmt::skip]
 
+#[rustfmt::skip]
 pub mod unrooted_must_root {
     /**
     ```