vendor the dependencies

There is a discrepancy of behavior of `github.com/urfave/cli` between
using go1.12 and go1.15, when the dependency is not present as vendored
source. Now this builds fine with go1.12

There are users of tar-split as a package. It is the hope that by adding
this vendored source it does not impact them depending on tar-split
itself.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/russross/blackfriday/v2/.travis.yml

@@ -0,0 +1,17 @@
+sudo: false
+language: go
+go:
+  - "1.10.x"
+  - "1.11.x"
+  - tip
+matrix:
+  fast_finish: true
+  allow_failures:
+    - go: tip
+install:
+  - # Do nothing. This is needed to prevent default install action "go get -t -v ./..." from happening here (we want it to happen inside script step).
+script:
+  - go get -t -v ./...
+  - diff -u <(echo -n) <(gofmt -d -s .)
+  - go tool vet .
+  - go test -v ./...