Added rpm tools to wercker pre build step

wercker.yml

@@ -12,7 +12,6 @@ build:
         name: build setup
         code: |
          go run build.go setup
-          sudo gem install fpm
     # Build the project
     - script:
         name: build
@@ -26,6 +25,8 @@ build:
     - script:
         name: create packages
         code: |
+          sudo gem install fpm
+          sudo apt-get install -y rpm
           go run build.go package
     # save packages
     - script: