add $DEVPLATFORM

this adds the above variable to allow building the nightly image on the (fast) native build platform

Dockerfile.nightly

@@ -1,8 +1,12 @@
 ## DEVELOPMENT IMAGE
-FROM node:15-alpine AS dev
+ARG DEVPLATFORM=${TARGETPLATFORM:-linux/amd64}
+FROM --platform=$DEVPLATFORM node:15-alpine AS dev
 
 # Install pre-requisites
-RUN apk add --no-cache git python3 build-base
+RUN case $DEVPLATFORM in \
+    *arm*) apk add --no-cache git python3 build-base ;; \
+    *)     apk add --no-cache git python3 ;; \
+    esac
 
 # Fetch and build tileboard master branch
 RUN mkdir /tileboard-source \