update docker/Dockerfile.

`npm install pnpm@7.30.0 -g` 修改为`npm install pnpm -g`指定7.30.0 版本导致出现ERR_INVALID_THIS异常，node版本过新与旧版pnpm不兼容

Signed-off-by: Willis <569869783@qq.com>

docker/Dockerfile

@@ -49,7 +49,7 @@ RUN export BUNDLE_FFMPEG=${BUNDLE_FFMPEG:-true} \
     \
     && _NPM_MIRROR_FLAG="" \
     && if [ "$USE_NPM_MIRROR"x = "true"x ]; then _NPM_MIRROR_FLAG="--registry=https://registry.npmmirror.com"; fi \
-    && npm install pnpm@7.30.0 -g $_NPM_MIRROR_FLAG \
+    && npm install pnpm -g $_NPM_MIRROR_FLAG \
     \
     && ((test "$BUNDLE_POETRY"x = "true"x \
     && apt-get update \