Fix compiling with C++14, due to changed operator T* -> operator bool semantics.
See also: https://bugs.gentoo.org/show_bug.cgi?id=593872

--- a/src/write.cpp
+++ b/src/write.cpp
@@ -196,6 +196,6 @@
 
   string str = to_string(precision, width, expn_width, 
       fmt, showpos, uppercase, fill);
-  return (s << str) != 0;
+  return static_cast<bool>(s << str);
 }