docs: Fix typos in slabtop.1, sysctl.8 and uptime.1

slabtop.1

@@ -90,7 +90,7 @@ requires a 2.4 or later kernel (specifically, a version 1.1 or later
 Kernel 2.2 should be supported in the future.
 .PP
 The slabtop statistic header is tracking how many bytes of slabs are being
-used and it not a measure of physical memory.  The 'Slab' field in the
+used and is not a measure of physical memory.  The 'Slab' field in the
 /proc/meminfo file is tracking information about used slab physical memory.
 .SH AUTHORS
 Written by Chris Rivera and Robert Love.

sysctl.8

@@ -143,8 +143,8 @@ The
 .B base_reachable_time
 and
 .B retrans_time
-are deprecated.  The sysctl command does not allow changing values of there
-parameters.  Users who insist to use deprecated kernel interfaces should values
+are deprecated.  The sysctl command does not allow changing values of these
+parameters.  Users who insist to use deprecated kernel interfaces should push values
 to /proc file system by other means.  For example:
 .PP
 echo 256 > /proc/sys/net/ipv6/neigh/eth0/base_reachable_time

uptime.1

@@ -32,7 +32,7 @@ show uptime in pretty format
 display this help text
 .TP
 \fB\-s\fR, \fB\-\-since\fR
-system up since, in yyyy-mm-dd MM:HH:SS format
+system up since, in yyyy-mm-dd HH:MM:SS format
 .TP
 \fB\-V\fR, \fB\-\-version\fR
 display version information and exit