fix bash commands in travis script

.travis.yml

@@ -15,14 +15,14 @@ branches:
 
 before_install:
   - sudo apt-get update
-  - sudo apt-get install gdb python$((python -c 'import sys; print("%d.%d" % sys.version_info[:2])'))-dbg || true
+  - sudo apt-get install gdb python$( python -c 'import sys; print("%d.%d" % sys.version_info[:2])' )-dbg || true
   - dpkg -l | grep gdb || true
 
 install: pip install .
 
 script:
-  - PYTHON="`python$((python -c 'import sys; print("%d.%d" % sys.version_info[:2])'))-dbg`"
-  - CFLAGS="-O0 -ggdb" $(($PYTHON -V >&2 && echo $PYTHON || echo python)) runtests.py -vv
+  - PYTHON="`python$( python -c 'import sys; print("%d.%d" % sys.version_info[:2])' )-dbg`"
+  - CFLAGS="-O0 -ggdb" $( $PYTHON -V >&2 && echo $PYTHON || echo python ) runtests.py -vv
 
 matrix:
   allow_failures: