Fix nvm update condition
Fix nvm update condition

Resolves https://github.com/travis-ci/travis-ci/issues/5900

Integer comparison with `-lt` considers operands with leading zeros to
be octal. This is a problem when nvm version number includes '8' or
'9'.

We solve this problem with leading the operands with `1`, forcing
decimal format.

jhass/travis-build,craigcitro/travis-build,kevmoo/travis-build,kevmoo/travis-build,craigcitro/travis-build,JuliaCI/travis-build,JuliaCI/travis-build,akoeplinger/travis-build,jhass/travis-build,andyli/travis-build,andyli/travis-build,akoeplinger/travis-build