Correct PROCESS_MAX_UID_DIGITS constant

The PROCESS_MAX_UID_DIGITS=19 introduced in
696f79fe50 doesn't make sense.
The `uid_t` type does not require to be signed in POSIX. If we are to
support 64 bits as the maximum size of `uid_t`, then
PROCESS_MAX_UID_DIGITS should be 20. (= floor(log10(UINT64_MAX)) + 1).

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

Process.h

@@ -293,7 +293,7 @@ extern uint8_t Process_fieldWidths[LAST_PROCESSFIELD];
 #define PROCESS_MIN_PID_DIGITS 5
 #define PROCESS_MAX_PID_DIGITS 19
 #define PROCESS_MIN_UID_DIGITS 5
-#define PROCESS_MAX_UID_DIGITS 19
+#define PROCESS_MAX_UID_DIGITS 20
 extern int Process_pidDigits;
 extern int Process_uidDigits;