.drone.yml: Give more resources to the JVM used by sbt

sbt runs up to `Runtime.getRuntime.availableProcessors` tasks in
parallel, on our CI that means 40 tasks, compilation tasks are the one
with the biggest footprint and the introduction of
`dotty-library-bootstrapped` and `dotty-compiler-bootstrapped` in this
PR means that sbt can now run more compilation tasks in parallel. To
prevent the JVM from exploding, we increase:
- The max heap size, from 1G to 4G
- The max code cache size, from 240M to 512M
- The max metaspace size, from 256M to 1G

Author: smarter

.drone.yml

@@ -5,7 +5,7 @@ pipeline:
     commands:
       - ln -s /var/cache/drone/scala-scala scala-scala
       - ./scripts/update-scala-library
-      - sbt -Ddotty.drone.mem=4096m -ivy /var/cache/drone/ivy2 "${TEST}"
+      - sbt -J-Xmx4096m -J-XX:ReservedCodeCacheSize=512m -J-XX:MaxMetaspaceSize=1024m -Ddotty.drone.mem=4096m -ivy /var/cache/drone/ivy2 "${TEST}"
 
 matrix:
   TEST: