Fix warnings about constants being too large.

format.cc

@@ -128,16 +128,16 @@ const uint64_t fmt::internal::POWERS_OF_10[] = {
   10000000,
   100000000,
   1000000000,
-  10000000000,
-  100000000000,
-  1000000000000,
-  10000000000000,
-  100000000000000,
-  1000000000000000,
-  10000000000000000,
-  100000000000000000,
-  1000000000000000000,
-  10000000000000000000u
+  10000000000ull,
+  100000000000ull,
+  1000000000000ull,
+  10000000000000ull,
+  100000000000000ull,
+  1000000000000000ull,
+  10000000000000000ull,
+  100000000000000000ull,
+  1000000000000000000ull,
+  10000000000000000000ull
 };
 
 void fmt::internal::ReportUnknownType(char code, const char *type) {