try libtommath from ubuntu

.travis.yml

@@ -11,12 +11,16 @@ addons:
     packages:
     - clang-3.8
 
+install:
+    - sudo apt-get update -qq
+    - sudo apt-get install libtommath-dev
+
 before_script:
   - gem install coveralls-lcov
   - curl http://ftp.de.debian.org/debian/pool/main/l/lcov/lcov_1.11.orig.tar.gz | tar xz
   - export PATH=$PATH:`pwd`/lcov-1.11/bin
   - curl -s https://packagecloud.io/install/repositories/libtom/packages/script.deb.sh | sudo bash
-  - sudo apt-get install libtfm-dev=0.13-5 libtommath-dev=1.0-4
+  - sudo apt-get install libtfm-dev=0.13-5
 
 matrix:
   fast_finish: true