Make javascript:build depend on yarn:install directly (#49)

jsbundling-rails depends on railties already, so yarn:install is
always available and this avoid problems with .rake files being loaded
in different orders.

Author: zarqman

lib/tasks/jsbundling/build.rake

@@ -1,6 +1,6 @@
 namespace :javascript do
   desc "Build your JavaScript bundle"
-  task :build do
+  task build: [ "yarn:install" ] do
     unless system "yarn build"
       raise "jsbundling-rails: Command build failed, ensure yarn is installed and `yarn build` runs without errors"
     end
@@ -14,7 +14,3 @@ if Rake::Task.task_defined?("test:prepare")
 elsif Rake::Task.task_defined?("db:test:prepare")
   Rake::Task["db:test:prepare"].enhance(["javascript:build"])
 end
-
-if Rake::Task.task_defined?("yarn:install")
-  Rake::Task["javascript:build"].enhance(["yarn:install"])
-end