Update pub run syntax and remove 404 images (dart-archive/markdown#625)

Author: andrechalella

pkgs/markdown/benchmark/input.md

@@ -85,14 +85,9 @@ void main() {
 
 ## Running Tests
 
-A single test file can be run just using `pub run test:test path/to/test.dart`
-(on Dart 1.10, this can be shortened to `pub run test path/to/test.dart`).
+A single test file can be run just using `dart run test path/to/test.dart`.
 
-![Single file being run via pub run"](https://raw.githubusercontent.com/dart-lang/test/master/image/test1.gif)
-
-Many tests can be run at a time using `pub run test:test path/to/dir`.
-
-![Directory being run via "pub run".](https://raw.githubusercontent.com/dart-lang/test/master/image/test2.gif)
+Many tests can be run at a time using `dart run test path/to/dir`.
 
 It's also possible to run a test on the Dart VM only by invoking it using `dart
 path/to/test.dart`, but this doesn't load the full test runner and will be
@@ -103,11 +98,11 @@ file. If you don't pass any paths, it will run all the test files in your
 `test/` directory, making it easy to test your entire application at once.
 
 By default, tests are run in the Dart VM, but you can run them in the browser as
-well by passing `pub run test:test -p chrome path/to/test.dart`.
+well by passing `dart run test -p chrome path/to/test.dart`.
 `test` will take care of starting the browser and loading the tests, and all
 the results will be reported on the command line just like for VM tests. In
-fact, you can even run tests on both platforms with a single command: `pub run
-test:test -p "chrome,vm" path/to/test.dart`.
+fact, you can even run tests on both platforms with a single command: `dart run
+test -p chrome,vm path/to/test.dart`.
 
 ### Restricting Tests to Certain Platforms
 

pkgs/markdown/test/version_test.dart

@@ -35,7 +35,7 @@ void main() {
       binVersion,
       pubspecContent['version'],
       reason: 'The version reported by bin/markdown.dart should match the '
-          'version in pubspec. Run `pub run build_runner build` to update.',
+          'version in pubspec. Run `dart run build_runner build` to update.',
     );
   });
 }