Merge pull request microsoft#24238 from bluelovers/patch-1

es2018 regexp dotAll

Author: mhegazy

lib/lib.es2018.regexp.d.ts

@@ -28,4 +28,9 @@ interface RegExpExecArray {
     groups?: {
         [key: string]: string
     }
-}
+}
+
+interface RegExp {
+    /** Returns a Boolean value indicating the state of the dotAll flag (s) used with a regular expression. Default is false. Read-only. */
+    readonly dotAll: boolean;
+}