Update TinyGsmClientSIM800.h

Set default alphabet for sendSMS

src/TinyGsmClientSIM800.h

@@ -655,6 +655,9 @@ public:
   bool sendSMS(const String& number, const String& text) {
     sendAT(GF("+CMGF=1"));
     waitResponse();
+    //Set GSM 7 bit default alphabet (3GPP TS 23.038)
+    sendAT(GF("+CSCS=\"GSM\""));
+    waitResponse();
     sendAT(GF("+CMGS=\""), number, GF("\""));
     if (waitResponse(GF(">")) != 1) {
       return false;