use new paper build system

Dockerfile

@@ -1,18 +1,20 @@
-FROM openjdk:11 as builder
+FROM openjdk:16-alpine as builder
+
+RUN apk --no-cache add \
+    patch \
+    maven \
+    git
 
 RUN git config --global user.email "papermcbuilder@vanwa.ch"
 RUN git config --global user.name "Vanwa papermc builder"
 
-RUN apt update && apt install -y \
-    patch \
-    maven
-
 ENV VERSION=f521a18a17f32997793b2d0b2ebcd7890f200fc8
 RUN git clone https://github.com/PaperMC/Paper.git
 
 WORKDIR /Paper
 RUN git checkout "$VERSION"
-RUN ./paper jar
+RUN ./gradlew applyPatches
+RUN ./gradlew reobfJar
 RUN mv /Paper/Paper-Server/target/paper-*.jar /Paper/Paper-Server/target/paper.jar
 
 FROM thallian/confd-env:latest
@@ -20,9 +22,11 @@ FROM thallian/confd-env:latest
 COPY --from=builder /Paper/Paper-Server/target/paper.jar /var/lib/minecraft/paper.jar
 
 RUN apk add --no-cache \
-    openjdk11-jre-headless \
     openssl
 
+RUN apk add --no-cache --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing \
+    openjdk16-jre-headless
+
 RUN addgroup minecraft -g 2222
 RUN adduser -u 2222 -h /var/lib/minecraft -D -G minecraft minecraft