Use arithmetic expansion in scripts, avoid bashisms
diff --git a/.travis.yml b/.travis.yml
index 0e79aa9..161f726 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@
 - clang
 - gcc
 before_install: sudo apt-get update
-install: sudo apt-get install bc gnutls-bin valgrind perl
+install: sudo apt-get install gnutls-bin valgrind perl
 script:
 - cmake -D CMAKE_BUILD_TYPE:String="Check" .
 - make