Fix some methods showing as virtual incorrectly (#21)

Fixes #20

Author: SeeminglyScience

src/ClassExplorer/SignatureWriter.cs

@@ -649,6 +649,11 @@ public SignatureWriter Modifiers(MethodBase method)
 
         if ((method.Attributes & MethodAttributes.NewSlot) is not 0)
         {
+            if (method.IsFinal)
+            {
+                return this;
+            }
+
             return Keyword("virtual").Space();
         }