Use correct changelog placeholder format

JPry · JPry · commit 5aef86fa169d · 2021-10-20T11:24:27.000-04:00
diff --git a/README.txt b/README.txt
@@ -57,5 +57,5 @@ Release and roadmap notes available on the [WooCommerce Developers Blog](hhttps:
 
 == Changelog ==
 
-= 1.0.0 - 2021-10-XX =
+= 1.0.0 - 2021-xx-xx =
 - Initial release
diff --git a/changelog.txt b/changelog.txt
@@ -1,4 +1,4 @@
 *** Pinterest for WooCommerce Changelog ***
 
-= 1.0.0 - 2021-10-XX =
+= 1.0.0 - 2021-xx-xx =
 - Initial release
