Configure shell to use bash

- Previously, we had installed bash, but the shell for RUN commands was still /bin/busybox; this broke the brace expansion loop for the retry logic while installing yarn and Pterodactyl dependencies

Author: Loki-101

Dockerfile

@@ -27,6 +27,7 @@ RUN apk update && apk add --no-cache \
     sed \
     musl-locales
 
+SHELL ["/bin/bash", "-c"]
 ENV LANG=C.UTF-8
 ENV LC_ALL=C.UTF-8