Fix LSB_RELEASE definition

${$(sw_vers -productVersion)%*.*})} results in
"bad substitution"

Author: BanzaiMan

.travis.yml

@@ -19,7 +19,7 @@ matrix:
       os: osx
       osx_image: xcode7.3
       env:
-        - RELEASE=sierra
+        - RELEASE=elcapitan
     - language: c
       os: osx
       osx_image: xcode6.4
@@ -46,7 +46,7 @@ install:
 
 before_script:
 - 'export INSTALL_DEST=${INSTALL_DEST:-/opt/python}'
-- 'export LSB_RELEASE=${LSB_RELEASE:-$(lsb_release -rs || echo ${$(sw_vers -productVersion)%*.*})}'
+- export LSB_RELEASE=$(lsb_release -rs 2>/dev/null || sw_vers -productVersion | sed 's/^\([0-9][0-9]*.[0-9][0-9]*\).*/\1/')
 - 'export OS_NAME=${OS_NAME:-$(lsb_release -is | tr "A-Z" "a-z" || echo "osx")}'
 - 'export ARCH=${ARCH:-$(uname -m)}'
 - 'export PACKAGES=${PACKAGES:-pip nose pytest mock wheel}'