use packagecloud repo to install tfm

.travis.yml

@@ -7,12 +7,13 @@ addons:
     packages:
     - binutils
     - libtommath-dev
-    - libtfm-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/tomsfastmath/script.deb.sh | sudo bash
+  - sudo apt-get install libtfm-dev=0.13-5
 
 matrix:
   fast_finish: true