graph/formats/rdf: work around unhelpful mechanical lawyer

graph/formats/rdf/rdf_test.go

@@ -21,7 +21,7 @@ func TestRDFWorkingGroupSuite(t *testing.T) {
 		"ntriple_tests.tar.gz",
 		"nquad_tests.tar.gz",
 	} {
-		suite, err := os.Open(file)
+		suite, err := os.Open(filepath.Join("testdata", file))
 		if err != nil {
 			t.Fatalf("Failed to open test suite in %q: %v", file, err)
 		}

graph/formats/rdf/testdata/LICENSE.md

@@ -1,6 +1,6 @@
 Test suite license
 
-This document refers to nquad_tests.tar.gz, ntriple_tests.tar.gz and normalization tests in testdata. The original files can be obtained here:
+This document refers to nquad_tests.tar.gz, ntriple_tests.tar.gz and normalization tests in this directory. The original files can be obtained here:
 
 - [nquad_tests.tar.gz](https://w3c.github.io/rdf-tests/nquads/TESTS.tar.gz)
 - [ntriple_tests.tar.gz](https://w3c.github.io/rdf-tests/ntriples/TESTS.tar.gz)