Declare Java 11 Requirement

When the logging library was moved from log4j to logback, the version of
logback used required Java 11 at runtime. I didn't notice this as I (and
I assume most of you given the lack of reports) don't use Java 8 as my
primary runtime any longer.

This commit documents the Java 11 requirement initially introduced with
ad8d673 back in January 2023.

build.gradle.kts

@@ -13,7 +13,7 @@ plugins {
 group = "io.zachbr"
 version = "1.6.3-SNAPSHOT"
 
-val targetJVM = JavaVersion.VERSION_1_8.toString()
+val targetJVM = JavaVersion.VERSION_11.toString()
 
 repositories {
     maven("https://m2.dv8tion.net/releases")

docs/Getting-Started.md

@@ -1,7 +1,7 @@
 Getting Started
 ===============
 
-Dis4IRC requires **Java 8** or newer to run, so make sure you have that
+Dis4IRC requires **Java 11** or newer to run, so make sure you have that
 installed before proceeding.
 
 Startup