Add NonValidationKeyword "else" on 201909 and 202012 (#592)

Author: ionutalex88

src/main/java/com/networknt/schema/Version201909.java

@@ -32,7 +32,8 @@ JsonMetaSchema getInstance() {
                         new NonValidationKeyword("contentMediaType"),
                         new NonValidationKeyword("contentEncoding"),
                         new NonValidationKeyword("examples"),
-                        new NonValidationKeyword("then")
+                        new NonValidationKeyword("then"),
+                        new NonValidationKeyword("else")
                 ))
                 .build();
     }

src/main/java/com/networknt/schema/Version202012.java

@@ -33,6 +33,7 @@ JsonMetaSchema getInstance() {
                         new NonValidationKeyword("contentEncoding"),
                         new NonValidationKeyword("examples"),
                         new NonValidationKeyword("then"),
+                        new NonValidationKeyword("else"),
                         new NonValidationKeyword("unevaluatedItems")
                 ))
                 .build();