travis: test nimble against the important packages list

Also update Nim to latest nightlies

Author: alaviss

.travis.yml

@@ -10,7 +10,7 @@ env:
   - BRANCH=0.20.2
   - BRANCH=1.0.0
   # This is the latest working Nim version against which Nimble is being tested
-  - BRANCH=#16c39f9b2edc963655889cfd33e165bfae91c96d
+  - BRANCH=#ab525cc48abdbbbed1f772e58e9fe21474f70f07
 
 cache:
   directories:
@@ -45,6 +45,7 @@ script:
   - nim c -r tester
   - cd ..
   - ./src/nimble install -y
+  - testament cat nimble-packages
 
 notifications:
   irc: "chat.freenode.net#nimbuild"