made battery and uptime work under MSYS2 / MINGW

.tmux.conf

@@ -281,7 +281,7 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 # $(find /sys/class/power_supply -maxdepth 1 -iname '*bat*')
 # EOF
 #       ;;
-#     *CYGWIN*)
+#     *CYGWIN*|*MSYS*|*MINGW*)
 #       while IFS= read -r line; do
 #         [ -z "$line" ] && continue
 #         if [ x"$discharging" != x"true" ]; then
@@ -548,7 +548,7 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 #       boot=$(sysctl -q -n kern.boottime | awk -F'[ ,:]+' '{ print $4 }')
 #       now=$(date +%s)
 #       ;;
-#     *Linux*|*CYGWIN*)
+#     *Linux*|*CYGWIN*|*MSYS*|*MINGW*)
 #       now=$(cut -d' ' -f1 < /proc/uptime)
 #       ;;
 #     *OpenBSD*)