Update katacoda scenarios

Signed-off-by: Javier Romero <[email protected]>

Author: jromero

katacoda/scenarios/buildpack-author-guide/build-app.md

@@ -122,7 +122,6 @@ pack build test-ruby-app --path ./ruby-sample-app --buildpack ./ruby-buildpack
 
 You will see the following output:
 
-<!-- test:assert=contains;ignore-lines=... -->
 ```
 ===> DETECTING
 ...

katacoda/scenarios/buildpack-author-guide/detection.md

@@ -33,7 +33,6 @@ pack build test-ruby-app --path ./ruby-sample-app --buildpack ./ruby-buildpack
 
 You should see the following output:
 
-<!-- test:assert=contains -->
 ```
 ===> ANALYZING
 Previous image with name "test-ruby-app" not found
@@ -43,7 +42,7 @@ examples/ruby 0.0.1
 ===> BUILDING
 ---> Ruby Buildpack
 ERROR: failed to build: exit status 1
-ERROR: failed to build: executing lifecycle
+ERROR: failed to build: executing lifecycle: failed with status code: 51
 ```
 
 Notice that `detect` now passes because there is a valid `Gemfile` in the Ruby app at `ruby-sample-app`, but now `build` fails because it is currently written to error out.