Make all pattern tokenizer parameters optional

elastic/elasticsearch-js#1967

Author: JoshMock

specification/_types/analysis/tokenizers.ts

@@ -96,9 +96,9 @@ export class PathHierarchyTokenizer extends TokenizerBase {
 
 export class PatternTokenizer extends TokenizerBase {
   type: 'pattern'
-  flags: string
-  group: integer
-  pattern: string
+  flags?: string
+  group?: integer
+  pattern?: string
 }
 
 export class StandardTokenizer extends TokenizerBase {