diff --git a/src/filter.ts b/src/filter.ts
index f9ea1b6..b28644f 100644
--- a/src/filter.ts
+++ b/src/filter.ts
@@ -59,7 +59,7 @@ export class Filter {
 
   private getPatterns(item: FilterItemYaml): string[] {
     if (Array.isArray(item)) {
-      return flat(item.map(i => this.getPatterns(i)))
+      return item.map(i => this.getPatterns(i)).flat()
     }
 
     if (typeof item === 'string') {
@@ -73,9 +73,3 @@ export class Filter {
     throw new Error(`Invalid filter YAML format: ${message}.`)
   }
 }
-
-// Creates a new array with all sub-array elements concatenated
-// In future could be replaced by Array.prototype.flat (supported on Node.js 11+)
-function flat<T>(arr: T[][]): T[] {
-  return arr.reduce((acc, val) => acc.concat(val), [])
-}