update travis to make htslib compiling

Author: dridk

.travis.yml

@@ -6,6 +6,7 @@ sudo: required
 before_install:
   - sudo add-apt-repository ppa:beineri/opt-qt58-trusty -y
   - sudo apt-get update
+  - git submodule update --init --recursive
 
 install:
   - sudo apt-get install qt58base qt58svg qt58charts-no-lgpl