fix: Dockerfile location in Makefile (#2254)

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## Overview

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As caught by @mojtaba-esk, the Makefile is using an invalid Dockerfile
location.

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- [ ] New and updated code has appropriate documentation
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Makefile

@@ -105,7 +105,7 @@ proto-format:
 ## build-docker: Build the celestia-appd docker image. Requires docker.
 build-docker:
 	@echo "--> Building Docker image"
-	$(DOCKER) build -t celestiaorg/celestia-app -f docker/Dockerfile .
+	$(DOCKER) build -t celestiaorg/celestia-app -f Dockerfile .
 .PHONY: build-docker
 
 ## lint: Run all linters: golangci-lint, markdownlint, hadolint, yamllint.