change min version to java 17

link to https://adoptium.net/de/temurin/releases/?version=17
add webrick to gems acording to jekyll/jekyll#8523

Signed-off-by: Markus Hochstein <markus.hochstein@software-hochstein.de>

Gemfile

@@ -10,3 +10,4 @@ source "https://rubygems.org"
 # Happy Jekylling!
 
 gem 'github-pages', group: :jekyll_plugins
+gem "webrick"

Gemfile.lock

@@ -260,12 +260,14 @@ GEM
       unf_ext
     unf_ext (0.0.8.2)
     unicode-display_width (1.8.0)
+    webrick (1.8.1)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
   github-pages
+  webrick
 
 BUNDLED WITH
    2.1.4

_tutorial/015-Prerequisite.md

@@ -14,7 +14,7 @@ Before you start any of the tutorials you must prepare your environment so that
 
 We need to run the following tools on your computer - without them you won't get very far at all.
 
-* [Java][java8], probably already got it? If not, this is a good time to get started! OSGi enRoute projects target Java 8 as a minimum version.
+* [Java][java17], probably already got it? If not, this is a good time to get started! OSGi enRoute projects target Java 17 as a minimum version.
 * [Maven][Maven], a popular build tool for Java applications with an enormous repository behind it. Make sure that you're on at least 3.3.9
 
 <div class="alert alert-warning">
@@ -133,7 +133,7 @@ If you start using enRoute you will likely create a number of workspaces. There
 
 We aren't currently aware of any challenges on Unix systems. Please [let us know](mailto:osgi-users@eclipse.org) if you have any!
 
-[java8]: http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
+[java17]: https://adoptium.net/de/temurin/releases/?version=17
 [Maven]: https://maven.apache.org
 [mars]: https://www.eclipse.org/downloads/
 [bndtools]: http://bndtools.org