Pin analyzer package so that we're consistent

See the comment in the patch for details.

packages/flutter/pubspec.yaml

@@ -16,6 +16,14 @@ dependencies:
   # on test.
   test: 0.12.6+1
 
+  # We have to pin analyzer to 0.27.1 because the flx package depends
+  # on pointycastle which depends on reflectable which depends on
+  # analyzer 0.27.1 and if we don't pin it here, then different
+  # packages end up bringing in different analyzer versions which
+  # results in 'flutter analyze' (which uses an entirely different
+  # analyzer, by the way!) complaining about the inconsistency.
+  analyzer: 0.27.1
+
   sky_engine:
     path: ../../bin/cache/pkg/sky_engine
   sky_services: