More changes to Travis Node versions
More changes to Travis Node versions

Remove iojs, since I don't expect issues which wouldn't be caught by the
other versions.

Add 0.8 as the earliest Node.js version which doesn't require building.

Plan to disable versions prior to 0.8 once we determine what the minimum
supported version of the module really is.

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

kevinoid/promised-read,kevinoid/promised-read,kevinoid/promised-read