fix bug on resolving import path for diskImportTempl

[jsteuer]

My GOPATH is/home/jsteuer/go:/home/jsteuer/go_dev. If I run packr2 the generated *-packr.go contains the following bad import.

// +build !skippackr
// Code generated by github.com/gobuffalo/packr/v2. DO NOT EDIT.

// You can use the "packr clean" command to clean up this,
// and any other packr generated files.
package template_index

import _ "_dev/src/github.com/jsteuer/myproject/packrd"

Because both paths are sharing the substring /home/jsteuer/go the algorithm to calculate the .Import path for diskImportTempl is depending on the order of the GOPATH. (If GO111MODULE=on the problem does not appears - thanks to #183). I think this is bug, so sorting the entries of the GOPATH solves this issue for me:

// +build !skippackr
// Code generated by github.com/gobuffalo/packr/v2. DO NOT EDIT.

// You can use the "packr clean" command to clean up this,
// and any other packr generated files.
package template_index

import _ "github.com/jsteuer/myproject/packrd"