Add the missing test for ERC721Holder (#1249)

* Add the missing test for ERC721Holder

* fix lint

* Move the holder test to a separate file

(cherry picked from commit 396680b8)

test/token/ERC721/ERC721Holder.test.js

+const ERC721Holder = artifacts.require('ERC721Holder.sol');
+const ERC721Mintable = artifacts.require('ERC721MintableBurnableImpl.sol');
+
+require('chai')
+  .should();
+
+contract('ERC721Holder', function ([creator]) {
+  it('receives an ERC721 token', async function () {
+    const token = await ERC721Mintable.new({ from: creator });
+    const tokenId = 1;
+    await token.mint(creator, tokenId, { from: creator });
+
+    const receiver = await ERC721Holder.new();
+    await token.approve(receiver.address, tokenId, { from: creator });
+    await token.safeTransferFrom(creator, receiver.address, tokenId);
+
+    (await token.ownerOf(tokenId)).should.be.equal(receiver.address);
+  });
+});