Disable tests that (still) require Internet access in the default bui…

…ld in the Makefile

test_caching_dns_resolver still requires Internet access. It has a pytest.mark decorator, but "make test" still runs it.

Now "make test" skips this test.

It's probably duplicative with the other tests because the MockedDnsResponseData resolver uses a dns.resolver.Resolver cache internally.

Fixes #128.

Makefile

@@ -17,7 +17,7 @@ typing:
 
 .PHONY: test
 test:
-	PYTHONPATH=.:$PYTHONPATH pytest --cov=email_validator
+	PYTHONPATH=.:$PYTHONPATH pytest --cov=email_validator -k "not network"
 
 .PHONY: testcov
 testcov: test