C++11-compliant fix for Windows

Author: pachadotdev

inst/include/cpp4r/r_bool.hpp

@@ -51,9 +51,8 @@ class r_bool {
   static constexpr int na = std::numeric_limits<int>::min();
 
   static constexpr int from_int(int value) noexcept {
-    if (value == static_cast<int>(FALSE)) return FALSE;
-    if (value == static_cast<int>(na)) return na;
-    return TRUE;
+    return (value == static_cast<int>(FALSE)) ? FALSE : 
+           (value == static_cast<int>(na)) ? na : TRUE;
   }
 
   int value_ = na;