[cron] Bump distribution date (2021-08-18)

Marlin/Version.h

@@ -41,7 +41,7 @@
  * here we define this default string as the date where the latest release
  * version was tagged.
  */
-//#define STRING_DISTRIBUTION_DATE "2021-08-17"
+//#define STRING_DISTRIBUTION_DATE "2021-08-18"
 
 /**
  * Defines a generic printer name to be output to the LCD after booting Marlin.

Marlin/src/inc/Version.h

@@ -42,7 +42,7 @@
  * version was tagged.
  */
 #ifndef STRING_DISTRIBUTION_DATE
-  #define STRING_DISTRIBUTION_DATE "2021-08-17"
+  #define STRING_DISTRIBUTION_DATE "2021-08-18"
 #endif
 
 /**