doc: update Travis CI environment information

Travis CI uses Ubuntu 12.04 LTS Server Edition now.
Merge pull request #122 from cosmo0920/fix-outdated-travis-info

doc: update Travis CI environment information

Patch by cosmo0920. Thanks!!!
between: support min/max cast
between: fix too much cast
Bump up version number to 3.1.1

3.1.0 ->
3.1.1

% make update-version NEW_VERSION=3.1.1
deb rpm: add 3.1.1 release entry

% make update-latest-release OLD_RELEASE=3.1.0 OLD_RELEASE_DATE=2013-11-29 NEW_RELEASE_DATE=2013-12-29
doc: update release version
rpm fedora: switch to Fedora 20
test: fix a typo

use_inddex ->
use_index
doc: add 3.1.1 release entry
windows: add missing MIN/MAX definitions on MinGW
Fix indent
Use ifndef
Indent
doc: update to Fedora 20