Merge branch 'update_xxhash' into 'develop'

Update xxHash source files

See merge request !40

src/glow/detail/xxHash/xxhash.cc

 /*
  * xxHash - Extremely Fast Hash algorithm
- * Copyright (C) 2012-2020 Yann Collet
+ * Copyright (C) 2012-2021 Yann Collet
  *
  * BSD 2-Clause License (https://www.opensource.org/licenses/bsd-license.php)
  *
@@ -37,7 +37,7 @@
  * xxhash.c instantiates functions defined in xxhash.h
  */
 
-#define XXH_STATIC_LINKING_ONLY /* access advanced declarations */
-#define XXH_IMPLEMENTATION      /* access definitions */
+#define XXH_STATIC_LINKING_ONLY   /* access advanced declarations */
+#define XXH_IMPLEMENTATION   /* access definitions */
 
 #include "xxhash.hh"