Makefile: Fix Fontconfig error

Define HOME env. variable to the working directory of the proto container
in order to avoid Fontconfig errors due to cache writing, like the
following:

dot ./images/devconfig.dot -Tpng -o ./images/devconfig.png
Fontconfig error: No writable cache directories
Fontconfig error: No writable cache directories

Setting HOME to the working directory fixes the problem.

Signed-off-by: Renê de Souza Pinto <rene@renesp.com.br>

Makefile

@@ -1,6 +1,6 @@
 proto-container:
 	docker build -f .devcontainer/Dockerfile -t eve-api-builder .
-	docker run --rm -v $(PWD):/src -w /src -u $$(id -u) eve-api-builder make proto
+	docker run --rm --env HOME=/src -v $(PWD):/src -w /src -u $$(id -u) eve-api-builder make proto
 
 proto-diagram:
 	protodot -inc /usr/local/include -src ./proto/config/devconfig.proto -output devconfig -generated ./images