support JDK 17

```
java.lang.ExceptionInInitializerError
at conscript.Conscript.run(conscript.scala:173)
at conscript.Conscript.run(conscript.scala:171)
at xsbt.boot.Launch$$anonfun$run$1.apply(Launch.scala:111)
at xsbt.boot.Launch$.withContextLoader(Launch.scala:131)
at xsbt.boot.Launch$.run(Launch.scala:111)
at xsbt.boot.Launch$$anonfun$apply$1.apply(Launch.scala:37)
at xsbt.boot.Launch$.launch(Launch.scala:120)
at xsbt.boot.Launch$.apply(Launch.scala:20)
at xsbt.boot.Boot$.runImpl(Boot.scala:56)
at xsbt.boot.Boot$.main(Boot.scala:18)
at xsbt.boot.Boot.main(Boot.scala)
Caused by: java.lang.IllegalStateException: java.lang.IllegalAccessException: class com.ning.http.util.ProxyHostnameChecker cannot access class sun.security.util.HostnameChecker (in module java.base) because module java.base does not export sun.security.util to unnamed module @63eef88a
at com.ning.http.util.ProxyHostnameChecker.getHostnameChecker(ProxyHostnameChecker.java:47)
at com.ning.http.util.ProxyHostnameChecker.(ProxyHostnameChecker.java:28)
at com.ning.http.util.DefaultHostnameVerifier.(DefaultHostnameVerifier.java:47)
at com.ning.http.client.AsyncHttpClientConfig.getHostnameVerifier(AsyncHttpClientConfig.java:392)
at com.ning.http.client.AsyncHttpClientConfig$Builder.(AsyncHttpClientConfig.java:977)
at dispatch.Http.unsafeConfigure(execution.scala:40)
at dispatch.Http.configure(execution.scala:32)
at conscript.Conscript$.(conscript.scala:10)
at conscript.Conscript$.(conscript.scala)
... 11 more
Caused by: java.lang.IllegalAccessException: class com.ning.http.util.ProxyHostnameChecker cannot access class sun.security.util.HostnameChecker (in module java.base) because module java.base does not export sun.security.util to unnamed module @63eef88a
at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:392)
at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:674)
at java.base/java.lang.reflect.Method.invoke(Method.java:560)
at com.ning.http.util.ProxyHostnameChecker.getHostnameChecker(ProxyHostnameChecker.java:39)
... 19 more
[error] [launcher] error during sbt launcher: java.lang.ExceptionInInitializerError
```

Reproduce the failure on JDK 17 and start from conscript.Conscript, dispatch.Http, and the com.ning.http.util.ProxyHostnameChecker stack-trace entries. Trace the initializer failure and verify that launching Conscript on JDK 17 no longer raises the module-access error.

Written by the indexing model from the issue text.