PROPOSAL: Support dynamic Node version

[notmessenger]

Currently we look for a hard-coded Node version in various scripts, for example if [[ ! "${PUBLISH_NODE_VERSION:-8.1.2}" =~ ^$TRAVIS_NODE_VERSION ]] in https://github.com/ciena-blueplanet/pr-bumper/blob/master/.travis/maybe-bump-version.sh#L10

I propose that we support the ability for the Node version to be set via a property so that when present it will be used in the scripts and when it is not then a/the default value is used. A likely candidate for where this property could be set is in the .pr-bumper.json file.

This will reduce the need for having to update the version of pr-bumper used in order to get a version of Node only if pr-bumper was released against/for the version desired.

[job13er]

I'm a little confused, isn't that exactly what PUBLISH_NODE_VERSION lets you do? The 8.1.2 is only used if PUBLISH_NODE_VERSION isn't provided in the environment.

[job13er]

(node@8.1.2) ~
[ameadows@PEW-AMEADOWS-02]$ echo ${PUBLISH_NODE_VERSION:-8.1.2}
8.1.2
(node@8.1.2) ~
[ameadows@PEW-AMEADOWS-02]$ export PUBLISH_NODE_VERSION=1.2.3
(node@8.1.2) ~
[ameadows@PEW-AMEADOWS-02]$ echo ${PUBLISH_NODE_VERSION:-8.1.2}
1.2.3

[notmessenger]

You are completely correct - I spaced on this.