Raise published jar's minimum Java from 17 to 21

Debian stable (trixie) now ships OpenJDK 21 by default, so 17 is no
longer the floor needed for broadest platform support. See #2055.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: soloturn

.github/workflows/gradle.yml

@@ -17,9 +17,9 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
         java: [26]
-        include: # test old java on one os only, upload from ubuntu java-17
+        include: # test old java on one os only, upload from ubuntu java-21
           - os: ubuntu-latest
-            java: 17
+            java: 21
             upload: true
 
     steps:

README.md

@@ -19,9 +19,9 @@ Download `ripme.jar` from the [latest release](https://github.com/ripmeapp/ripme
 
 ## Minimum Requirements
 
-Requires Java 17 or later to run. RipMe has been tested on and is confirmed working on Windows, Linux, and Mac.
+Requires Java 21 or later to run. RipMe has been tested on and is confirmed working on Windows, Linux, and Mac.
 
-Java 17 is the most modern possible Java version that allows us to support the most platforms. See [thread](https://github.com/RipMeApp/ripme/pull/2057#issuecomment-2571472016).
+Java 21 is the most modern possible Java version that allows us to support the most platforms; it's the default JDK on current Debian stable. See [thread](https://github.com/RipMeApp/ripme/pull/2057#issuecomment-2571472016) and [issue #2055](https://github.com/RipMeApp/ripme/issues/2055).
 
 ## Supported Sites