Fix tests by using new location of kingpin/v2 package.

[sam-fredrickson]

I tried to run the tests, but got errors because of the kingpin.v2 package.

$ go test ./...
# github.com/turnage/graw/cmd/act
cmd/act/act.go:10:2: no required module provides package gopkg.in/alecthomas/kingpin.v2; to add it:
	go get gopkg.in/alecthomas/kingpin.v2
FAIL	github.com/turnage/graw/cmd/act [setup failed]
# github.com/turnage/graw/cmd/feed
cmd/act/act.go:10:2: no required module provides package gopkg.in/alecthomas/kingpin.v2; to add it:
	go get gopkg.in/alecthomas/kingpin.v2
FAIL	github.com/turnage/graw/cmd/feed [setup failed]
ok  	github.com/turnage/graw	(cached)
?   	github.com/turnage/graw/botfaces	[no test files]
ok  	github.com/turnage/graw/reddit	(cached)
ok  	github.com/turnage/graw/streams	(cached)
ok  	github.com/turnage/graw/streams/internal/monitor	(cached)
ok  	github.com/turnage/graw/streams/internal/rsort	(cached)
FAIL

Next I tried getting that package, but found that it has been moved.

$ go get gopkg.in/alecthomas/kingpin.v2
go: gopkg.in/alecthomas/kingpin.v2@upgrade (v2.4.0) requires gopkg.in/alecthomas/kingpin.v2@v2.4.0: parsing go.mod:
        module declares its path as: github.com/alecthomas/kingpin/v2
                but was required as: gopkg.in/alecthomas/kingpin.v2

So, I changed the two files that used the old path with the new one, and now the tests pass.

$ go test ./...
ok  	github.com/turnage/graw	(cached)
?   	github.com/turnage/graw/botfaces	[no test files]
?   	github.com/turnage/graw/cmd/act	[no test files]
?   	github.com/turnage/graw/cmd/feed	[no test files]
ok  	github.com/turnage/graw/reddit	(cached)
ok  	github.com/turnage/graw/streams	(cached)
ok  	github.com/turnage/graw/streams/internal/monitor	(cached)
ok  	github.com/turnage/graw/streams/internal/rsort	(cached)

[turnage]

Thank you!