replace limits.h with climits

The former was deprecated with C++14. The standard says they are the same
with one exception:

The header<climits>defines all macros the same as the C standard library
header<limits.h>.

[Note:The types of the constants defined by macros in<climits>are not
required to match the types to which themacros refer.— end note]

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/db/update/InotifySource.cxx

@@ -25,10 +25,10 @@
 #include "Log.hxx"
 
 #include <cerrno>
+#include <climits>
 
 #include <sys/inotify.h>
 #include <stdint.h>
-#include <limits.h>
 
 bool
 InotifySource::OnSocketReady(gcc_unused unsigned flags) noexcept