build.sh is careless with encrypted variables

[ndw]

This feels like it should be a bug on travis-build, but that repo doesn't seem to accept issues.

If you encrypt an environment variable that contains a ")", travis falls over:

$ export DELTA_PASS=[secure]
/home/travis/build.sh: eval: line 41: syntax error near unexpected token `)'
/home/travis/build.sh: eval: line 41: `export DELTA_PASS=7^xxx1s)'

[BanzaiMan]

Please use the issue tracker in the main repository in the future: https://github.com/travis-ci/travis-ci/issues

This is a known issue and documented in http://docs.travis-ci.com/user/encryption-keys/#Note-on-escaping-certain-symbols