vendor: add missing deps and remove go get in .travis.yml

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

vendor/github.com/nightlyone/lockfile/lockfile_unix.go

@@ -0,0 +1,20 @@
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package lockfile
+
+import (
+	"os"
+	"syscall"
+)
+
+func isRunning(pid int) (bool, error) {
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		return false, err
+	}
+
+	if err := proc.Signal(syscall.Signal(0)); err != nil {
+		return false, nil
+	}
+	return true, nil
+}