Build docker image for CI

CPU image

docker build -t dgl-cpu -f Dockerfile.ci_cpu .

GPU image

docker build -t dgl-gpu -f Dockerfile.ci_gpu .

Lint image

docker build -t dgl-lint -f Dockerfile.ci_lint .

CPU image for kg

wget https://data.dgl.ai/dataset/FB15k.zip -P install/
docker build -t dgl-cpu:torch-1.2.0 -f Dockerfile.ci_cpu_torch_1.2.0 .

GPU image for kg

wget https://data.dgl.ai/dataset/FB15k.zip -P install/
docker build -t dgl-gpu:torch-1.2.0 -f Dockerfile.ci_gpu_torch_1.2.0 .