Specify int sizes

src/TinyGsmClientA6.h

@@ -318,7 +318,7 @@ class TinyGsmA6
   }
 
   // 0-9,*,#,A,B,C,D
-  bool dtmfSendImpl(char cmd, unsigned duration_ms = 100) {
+  bool dtmfSendImpl(char cmd, uint8_t duration_ms = 100) {
     duration_ms = constrain(duration_ms, 100, 1000);
 
     // The duration parameter is not working, so we simulate it using delay..

src/TinyGsmClientESP8266.h

@@ -19,7 +19,7 @@
 #define GSM_NL "\r\n"
 static const char GSM_OK[] TINY_GSM_PROGMEM    = "OK" GSM_NL;
 static const char GSM_ERROR[] TINY_GSM_PROGMEM = "ERROR" GSM_NL;
-static unsigned   TINY_GSM_TCP_KEEP_ALIVE      = 120;
+static uint8_t TINY_GSM_TCP_KEEP_ALIVE = 120;
 
 // <stat> status of ESP8266 station interface
 // 2 : ESP8266 station connected to an AP and has obtained IP