JAVA_OPTIONS breaks jetty start

Docker image: jetty:10.0.13-jdk11

If I have the following compose.yml file :

```
services:
test:
container_name: test
image: jetty:10.0.13-jdk11
volumes:
- ./someapp.war:/var/lib/jetty/webapps/ROOT.war
ports:
- '127.0.0.1:8080:8080'
```

Everything works fine. But if I just try to add JAVA_OPTIONS to it, like this:

```
services:
test:
container_name: test
image: jetty:10.0.13-jdk11
volumes:
- ./someapp.war:/var/lib/jetty/webapps/ROOT.war
ports:
- '127.0.0.1:8080:8080'
environment:
- JAVA_OPTIONS='-Xmx1g'
```

then the container exists right away with the error:

```
test | Error: Could not find or load main class '-Xmx1g'
test | Caused by: java.lang.ClassNotFoundException: '-Xmx1g'
test exited with code 1
```

Inside the container, when the bug happens, the file `/var/lib/jetty/jetty.start` is empty.