Remove any dependency on $GOPATH

Previously, we were running a small q.sh script at
$GOPATH/src/github.com/y0ssar1an/q/q.sh. With Go 1.12, $GOPATH is no longer a
requirement. We can't count on q.sh being at that path. This change just takes
the code that was in q.sh and moves it to the qq() function shown in the
README. Users should update their shell configs.

Switch from dep to Go modules

Update golangci-lint.
Disable the scopelint linter.

Replace individual linters with golangci-lint

Add .golangci.yml config file for golangci-lint. Simplify the Travis config and
Gopkg.toml because now there is only one linter to go get. Don't vendor
golangci-lint because dep fetches the wrong versions of golangci-lint's
dependencies.

Update golint

Change import path from github.com/golang/lint to golang.org/x/lint.

Revendor using the dep tool

Removes the unusued kr/pty pkg from vendor/.

Merge branch 'develop' of https://github.com/y0ssar1an/q

Print shortFile instead of abs path to current file