Fix another signed unsigned comparison warning.

test/unit/utglTF2ImportExport.cpp

@@ -327,7 +327,7 @@ TEST_F(utglTF2ImportExport, importglTF2PrimitiveModeTrianglesFan) {
     EXPECT_EQ(scene->mMeshes[0]->mNumVertices, 4u);
     EXPECT_EQ(scene->mMeshes[0]->mNumFaces, 2u);
     std::array<unsigned int, 3> f1 = {{ 0u, 3u, 2u }};
-    EXPECT_EQ(scene->mMeshes[0]->mFaces[0].mNumIndices, 3);
+    EXPECT_EQ(scene->mMeshes[0]->mFaces[0].mNumIndices, 3u );
     for (size_t i = 0; i < 3; ++i) {
         EXPECT_EQ(scene->mMeshes[0]->mFaces[0].mIndices[i], f1[i]);
     }