MSVC version greater 17.7.1 would give errors for civil_time_detail.h (…

…google#273)

The compiler cannot identify (max) as a trick to prevent MACRO treatment. A trailing return type fixes this.

include/cctz/civil_time_detail.h

@@ -367,11 +367,11 @@ class civil_time {
       : civil_time(ct.f_) {}
 
   // Factories for the maximum/minimum representable civil_time.
-  static CONSTEXPR_F civil_time (max)() {
+  static CONSTEXPR_F auto (max)() -> civil_time {
     const auto max_year = (std::numeric_limits<std::int_least64_t>::max)();
     return civil_time(max_year, 12, 31, 23, 59, 59);
   }
-  static CONSTEXPR_F civil_time (min)() {
+  static CONSTEXPR_F auto (min)() -> civil_time {
     const auto min_year = (std::numeric_limits<std::int_least64_t>::min)();
     return civil_time(min_year, 1, 1, 0, 0, 0);
   }