Use TRAVIS_BRANCH - it is always set

Author: m-messiah

.travis.yml

@@ -9,7 +9,7 @@ before_install:
   - cpanm --local-lib=~/perl5 --quiet local::lib
   - eval $(perl -I ~/perl5/lib/perl5/ -Mlocal::lib)
   - cpanm --local-lib=~/perl5 --quiet --notest Test::Nginx::Socket
-  - echo "const VERSION = \"${TRAVIS_TAG}\"" >> version.go
+  - echo "const VERSION = \"${TRAVIS_BRANCH}\"" >> version.go
 script:
   - go build -o ip2geo
   - ./ip2geo -version