Fix the way year is parsed from header

sohstationviewer/model/reftek/rt130_experiment/reftek.py

@@ -97,7 +97,7 @@ def get_rt130_packet_header(rt130_packet: bytes,
         raise RT130ParseError
 
     experiment_number = unpacker.unpack('b', rt130_packet[2:3])[0]
-    year = unpacker.unpack('b', rt130_packet[3:4])[0]
+    year = int(rt130_packet[3:4].hex())
     # A call to str.upper() is needed because bytes.hex() makes any
     # hexadecimal letter (i.e. ABCDEF) lowercase, while we want them to be
     # uppercase for display purpose.