Validate the concat::fragment order parameter as string||integer

This is to work around a validation issue that arises under the 3.x future
parser, as proper numeric types have been introduced (ie, not all scalar values
are strings).  Users have come to expect to to be able to pass in unquoted
integer values to the order parameter which will fail to validate as a string
when the future parser is enabled.
raise the "low bar" travis puppet version to 2.7.6

It appears that puppet 2.7.3 does not play nicely with stdlib 4.2.0.
add .vagrant to .gitignore
Merge pull request #185 from jhoblitt/feature/fragment_order_validation

Validate the concat::fragment order parameter as string||integer