TBR: Fixing the apptests by pinning the version so
breaking changes don't creep in.

Change-Id: I7fefb3e385c6bab762d3fa1b551adc0e4d76a96d
diff --git a/pubspec.yaml b/pubspec.yaml
index 1e102c9..916e77b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -7,6 +7,6 @@
   mojo_sdk: '>=0.2.19 <0.3.0'
 dev_dependencies:
   dart_style: any
-  mojo_apptest: any
+  mojo_apptest: 0.2.27
 environment:
   sdk: '>=1.12.0 <2.0.0'