update Unicode include files to version 15.0.0

enc/unicode/15.0.0/casefold.h

@@ -1,15 +1,15 @@
 /* DO NOT EDIT THIS FILE. */
-/* Generated by enc/unicode/case-folding.rb */
+/* Generated by enc-case-folding.rb */
 
 #if defined ONIG_UNICODE_VERSION_STRING && !( \
-      ONIG_UNICODE_VERSION_MAJOR == 14 && \
+      ONIG_UNICODE_VERSION_MAJOR == 15 && \
       ONIG_UNICODE_VERSION_MINOR == 0 && \
       ONIG_UNICODE_VERSION_TEENY == 0 && \
       1)
 # error ONIG_UNICODE_VERSION_STRING mismatch
 #endif
-#define ONIG_UNICODE_VERSION_STRING "14.0.0"
-#define ONIG_UNICODE_VERSION_MAJOR 14
+#define ONIG_UNICODE_VERSION_STRING "15.0.0"
+#define ONIG_UNICODE_VERSION_MAJOR 15
 #define ONIG_UNICODE_VERSION_MINOR 0
 #define ONIG_UNICODE_VERSION_TEENY 0