Pin pytorch-lightning version to 1.7.7 to fix crash

Attempts to use easy_train.sh crash with this error:

AttributeError: `Trainer.root_gpu` was deprecated in
v1.6 and is no longer accessible as of v1.8. Please use
`Trainer.strategy.root_device.index` instead.

Support for Trainer.root_gpu was removed in:
Lightning-AI/pytorch-lightning#11994

Dockerfile

@@ -11,10 +11,10 @@ RUN apt install -y python3 python3-dev python3-pip
 RUN DEBIAN_FRONTEND=noninteractive TZ=Etc/UTC apt install -y cmake
 
 RUN pip3 install --no-cache --upgrade pip setuptools
-RUN --mount=type=cache,target=/root/.cache/pip \
-  pip3 install torch --extra-index-url https://download.pytorch.org/whl/cu117
-RUN --mount=type=cache,target=/root/.cache/pip \
-  pip3 install python-chess==0.31.4 psutil asciimatics pytorch-lightning GPUtil cupy-cuda117
+RUN --mount=type=cache,target=/root/.cache/pip pip3 install \
+  torch --extra-index-url https://download.pytorch.org/whl/cu117
+RUN --mount=type=cache,target=/root/.cache/pip pip3 install \
+  python-chess==0.31.4 psutil asciimatics pytorch-lightning==1.7.7 GPUtil cupy-cuda117
 
 RUN ln -sf python3 /usr/bin/python