Update go-license-detector to v3

go-license-detector v2 was depending on an old version of
gopkg.in/src-d/go-git, and unfortunately the latest version
broke compatibility unexpectedly. This made golicense
unnecessarily difficult to build in repositories which otherwise
used gopkg.in/src-d/go-git. Upgrading to v3 removes these problems.
See src-d/go-git#1262 for full context.

It also allows us to remove a whole lot of packages from go.mod
in general.

go.mod

@@ -4,53 +4,25 @@ go 1.13
 
 require (
 	github.com/360EntSecGroup-Skylar/excelize v1.4.0
-	github.com/alcortesm/tgz v0.0.0-20161220082320-9c5fe88206d7 // indirect
-	github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239 // indirect
 	github.com/davecgh/go-spew v1.1.1
-	github.com/dgryski/go-metro v0.0.0-20180109044635-280f6062b5bc // indirect
-	github.com/dgryski/go-minhash v0.0.0-20170608043002-7fe510aff544 // indirect
-	github.com/dgryski/go-spooky v0.0.0-20170606183049-ed3d087f40e2 // indirect
-	github.com/ekzhu/minhash-lsh v0.0.0-20171225071031-5c06ee8586a1 // indirect
-	github.com/emirpasic/gods v1.12.0 // indirect
 	github.com/fatih/color v1.7.0
-	github.com/flynn/go-shlex v0.0.0-20150515145356-3f9db97f8568 // indirect
-	github.com/gliderlabs/ssh v0.2.2 // indirect
 	github.com/google/go-github/v18 v18.2.0
 	github.com/gosuri/uilive v0.0.0-20170323041506-ac356e6e42cd
 	github.com/hashicorp/go-multierror v1.0.0
 	github.com/hashicorp/hcl2 v0.0.0-20181111172936-0467c0c38ca2
 	github.com/hhatto/gorst v0.0.0-20181029133204-ca9f730cac5b // indirect
-	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
-	github.com/jdkato/prose v1.1.0 // indirect
-	github.com/kevinburke/ssh_config v0.0.0-20180830205328-81db2a75821e // indirect
 	github.com/mattn/go-colorable v0.0.9 // indirect
 	github.com/mattn/go-isatty v0.0.4 // indirect
-	github.com/mitchellh/go-homedir v1.0.0 // indirect
 	github.com/mitchellh/go-spdx v0.1.0
 	github.com/mohae/deepcopy v0.0.0-20170929034955-c48cc78d4826 // indirect
 	github.com/montanaflynn/stats v0.0.0-20180911141734-db72e6cae808 // indirect
-	github.com/neurosnap/sentences v1.0.6 // indirect
-	github.com/pelletier/go-buffruneio v0.2.0 // indirect
-	github.com/pkg/errors v0.8.0 // indirect
 	github.com/rsc/goversion v1.2.0
 	github.com/sebdah/goldie v0.0.0-20180424091453-8784dd1ab561
 	github.com/shogo82148/go-shuffle v0.0.0-20180218125048-27e6095f230d // indirect
-	github.com/shurcooL/sanitized_anchor_name v0.0.0-20170918181015-86672fcb3f95 // indirect
-	github.com/src-d/gcfg v1.4.0 // indirect
-	github.com/stretchr/objx v0.1.1 // indirect
-	github.com/stretchr/testify v1.2.2
-	github.com/xanzy/ssh-agent v0.2.0 // indirect
-	golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2
+	github.com/stretchr/testify v1.3.0
+	golang.org/x/crypto v0.0.0-20190701094942-4def268fd1a4
 	golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be
-	golang.org/x/tools v0.0.0-20190312151545-0bb0c0a6e846
+	golang.org/x/tools v0.0.0-20190729092621-ff9f1409240a
 	gonum.org/v1/netlib v0.0.0-20191031114514-eccb95939662 // indirect
-	gopkg.in/neurosnap/sentences.v1 v1.0.6 // indirect
-	gopkg.in/russross/blackfriday.v2 v2.0.0 // indirect
-	gopkg.in/src-d/go-billy-siva.v4 v4.2.2 // indirect
-	gopkg.in/src-d/go-billy.v4 v4.3.0 // indirect
-	gopkg.in/src-d/go-git-fixtures.v3 v3.5.0 // indirect
-	gopkg.in/src-d/go-git.v4 v4.7.0 // indirect
-	gopkg.in/src-d/go-license-detector.v2 v2.0.0-20180510072912-da552ecf050b
-	gopkg.in/src-d/go-siva.v1 v1.3.0 // indirect
-	gopkg.in/warnings.v0 v0.1.2 // indirect
+	gopkg.in/src-d/go-license-detector.v3 v3.0.2
 )