[DOCS] Fix class list in class diagram (#1301)

- adapt the sorting to how the diagram generator sorts
- add `SpecificityCalculator` which had been missing

Author: oliverklee

README.md

@@ -713,12 +713,14 @@ classDiagram
     }
     class SourceException {
     }
+    class SpecificityCalculator {
+    }
+    class URL {
+    }
     class UnexpectedEOFException {
     }
     class UnexpectedTokenException {
     }
-    class URL {
-    }
     class Value {
         <<abstract>>
     }