#1361 Sloeber plugin won't install on 2021-06 after most recent update

Added eclipse release repository
Added jre location

Author: wimjongman

io.sloeber.updatesite/category.xml

@@ -17,6 +17,8 @@
       </description>
    </category-def>
    <repository-reference location="https://download.eclipse.org/releases/latest/" enabled="true" />
+   <repository-reference location="https://download.eclipse.org/eclipse/updates/latest" enabled="true" />
+   <repository-reference location="https://download.eclipse.org/justj/jres/15/updates/release/latest/" enabled="true" />
    <repository-reference location="https://download.eclipse.org/technology/babel/update-site/latest/" enabled="true" />
    <repository-reference location="https://download.eclipse.org/nebula/releases/latest/" enabled="true" />
 </site>