enhance indentation class diagram test: abstract class and interface

test/plantuml-indentation-class-test.el

@@ -89,6 +89,14 @@ These code examples are taken from www.plantuml.com"
             int size()
             }
 
+            abtract class AbstractC {
+            int size()
+            }
+
+            interface InterfaceC {
+            int size()
+            }
+
             package \"Classic Collections\" #DDDDDD {
             Object <|-- ArrayList
             }
@@ -229,6 +237,14 @@ class Foo<? extends Element> {
   int size()
 }
 
+abtract class AbstractC {
+  int size()
+}
+
+interface InterfaceC {
+  int size()
+}
+
 package \"Classic Collections\" #DDDDDD {
   Object <|-- ArrayList
 }