[Build] Adds caching to shippable

Which should speed up things. Also reverts to the old version of the
file after several tests with containers.

Author: JJ

shippable.yml

@@ -1,10 +1,11 @@
 build:
-  pre_ci_boot:
-    image_name: jjmerelo/perl6-doc-shippable
-    pull: true
-
+  cache: true
+  
   ci:
-    - P6_DOC_TEST_VERBOSE=1 prove -e perl6 t
-
-
+    - wget https://github.com/nxadm/rakudo-pkg/releases/download/v2018.03-01/rakudo-pkg-Ubuntu14.04_2018.03-01_amd64.deb
+    - dpkg -i *.deb
+    - apt-get update && apt-get install libssl-dev
+    - PATH=~/.perl6/bin:/opt/rakudo-pkg/bin:$PATH && export PATH
+    - install-zef-as-user && zef --/tap-harness --depsonly install .
+    - P6_DOC_TEST_VERBOSE=1 make test