Fix memory statistics on Alpine Linux (#93)

On Alpine Linux, free doesn't have a -t option. This commit removes it.

Resolves hjelev/rpi-mqtt-monitor#91

src/rpi-cpu2mqtt.py

@@ -71,7 +71,7 @@ def check_voltage():
 
 
 def check_swap():
-    full_cmd = "free -t |grep -i swap | awk 'NR == 1 {print $3/$2*100}'"
+    full_cmd = "free | grep -i swap | awk 'NR == 1 {print $3/$2*100}'"
     swap = subprocess.Popen(full_cmd, shell=True, stdout=subprocess.PIPE).communicate()[0]
     swap = round(float(swap.decode("utf-8").replace(",", ".")), 1)
 
@@ -79,7 +79,7 @@ def check_swap():
 
 
 def check_memory():
-    full_cmd = "free -t | awk 'NR == 2 {print $3/$2*100}'"
+    full_cmd = "free | grep -i mem | awk 'NR == 1 {print $3/$2*100}'"
     memory = subprocess.Popen(full_cmd, shell=True, stdout=subprocess.PIPE).communicate()[0]
     memory = round(float(memory.decode("utf-8").replace(",", ".")))