pkg/util/{filepath.go,shortid_generator.go}: Fix golint issues

See,
$ gometalinter --vendor --deadline 10m --disable-all --enable=golint  ./...
filepath.go:12:5⚠️ error var WalkSkipDir should have name of the form ErrFoo (golint)
shortid_generator.go:11:5⚠️ var validUidPattern should be validUIDPattern (golint)
shortid_generator.go:19:6⚠️ func IsValidShortUid should be IsValidShortUID (golint)
shortid_generator.go:24:6⚠️ func GenerateShortUid should be GenerateShortUID (golint)

pkg/services/sqlstore/dashboard.go

@@ -27,7 +27,7 @@ func init() {
 	bus.AddHandler("sql", HasEditPermissionInFolders)
 }
 
-var generateNewUid func() string = util.GenerateShortUid
+var generateNewUid func() string = util.GenerateShortUID
 
 func SaveDashboard(cmd *m.SaveDashboardCommand) error {
 	return inTransaction(func(sess *DBSession) error {

pkg/services/sqlstore/dashboard_test.go

@@ -106,7 +106,7 @@ func TestDashboardDataAccess(t *testing.T) {
 					if timesCalled <= 2 {
 						return savedDash.Uid
 					}
-					return util.GenerateShortUid()
+					return util.GenerateShortUID()
 				}
 				cmd := m.SaveDashboardCommand{
 					OrgId: 1,
@@ -119,7 +119,7 @@ func TestDashboardDataAccess(t *testing.T) {
 				err := SaveDashboard(&cmd)
 				So(err, ShouldBeNil)
 
-				generateNewUid = util.GenerateShortUid
+				generateNewUid = util.GenerateShortUID
 			})
 
 			Convey("Should be able to create dashboard", func() {