rename 'Mac OS X' to 'macOS'

From the the release of macOS Sierra (Version 10.12) the Macintosh
operating system is called 'macOS'

doc/chrony.conf.adoc

@@ -1428,7 +1428,7 @@ cannot be used with the <<rtcfile,*rtcfile*>> directive.
 +
 On Linux, the RTC copy is performed by the kernel every 11 minutes.
 +
-On Mac OS X, <<chronyd,*chronyd*>> will perform the RTC copy every 60 minutes
+On macOS, <<chronyd,*chronyd*>> will perform the RTC copy every 60 minutes
 when the system clock is in a synchronised state.
 +
 On other systems this directive does nothing.
@@ -1786,8 +1786,8 @@ pidfile /run/chronyd.pid
 
 [[sched_priority]]*sched_priority* _priority_::
 On Linux, the *sched_priority* directive will select the SCHED_FIFO real-time
-scheduler at the specified priority (which must be between 0 and 100). On Mac
-OS X, this option must have either a value of 0 (the default) to disable the
+scheduler at the specified priority (which must be between 0 and 100). On
+macOS, this option must have either a value of 0 (the default) to disable the
 thread time constraint policy or 1 for the policy to be enabled. Other systems
 do not support this option.
 +
@@ -1802,7 +1802,7 @@ wait for the scheduler to get around to running it. You should not use this
 unless you really need it. The *sched_setscheduler(2)* man page has more
 details.
 +
-On Mac OS X, this directive uses the *thread_policy_set()* kernel call to
+On macOS, this directive uses the *thread_policy_set()* kernel call to
 specify real-time scheduling. As noted for Linux, you should not use this
 directive unless you really need it.
 
@@ -1811,7 +1811,7 @@ The *user* directive sets the name of the system user to which *chronyd* will
 switch after start in order to drop root privileges.
 +
 On Linux, *chronyd* needs to be compiled with support for the *libcap* library.
-On Mac OS X, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
+On macOS, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
 The child process retains root privileges, but can only perform a very limited
 range of privileged system calls on behalf of the parent.
 +

doc/chronyd.adoc

@@ -115,7 +115,7 @@ after start in order to drop root privileges. It overrides the
 <<chrony.conf.adoc#user,*user*>> directive (default _@DEFAULT_USER@_).
 +
 On Linux, *chronyd* needs to be compiled with support for the *libcap* library.
-On Mac OS X, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
+On macOS, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
 The child process retains root privileges, but can only perform a very limited
 range of privileged system calls on behalf of the parent.
 
@@ -134,7 +134,7 @@ killed even in normal operation.
 
 *-P* _priority_::
 On Linux, this option will select the SCHED_FIFO real-time scheduler at the
-specified priority (which must be between 0 and 100). On Mac OS X, this option
+specified priority (which must be between 0 and 100). On macOS, this option
 must have either a value of 0 (the default) to disable the thread time
 constraint policy or 1 for the policy to be enabled. Other systems do not
 support this option.

doc/faq.adoc

@@ -61,8 +61,8 @@ that.
 In order to keep the real-time clock (RTC) close to the true time, so the
 system time is reasonably close to the true time when it's initialized on the
 next boot from the RTC, the `rtcsync` directive enables a mode in which the
-system time is periodically copied to the RTC. It is supported on Linux and Mac
-OS X.
+system time is periodically copied to the RTC. It is supported on Linux and
+macOS.
 
 If you want to use public NTP servers from the
 http://www.pool.ntp.org/[pool.ntp.org] project, the minimal _chrony.conf_ file