Reinit updater md5 related fields (#4260)

MD5 cleanup on begin
Typos

libraries/Update/src/Update.h

@@ -90,12 +90,12 @@ class UpdateClass {
     bool setMD5(const char * expected_md5);
 
     /*
-      returns the MD5 String of the sucessfully ended firmware
+      returns the MD5 String of the successfully ended firmware
     */
     String md5String(void){ return _md5.toString(); }
 
     /*
-      populated the result with the md5 bytes of the sucessfully ended firmware
+      populated the result with the md5 bytes of the successfully ended firmware
     */
     void md5(uint8_t * result){ return _md5.getBytes(result); }
 

libraries/Update/src/Updater.cpp

@@ -115,6 +115,8 @@ bool UpdateClass::begin(size_t size, int command, int ledPin, uint8_t ledOn) {
 
     _reset();
     _error = 0;
+    _target_md5 = emptyString;
+    _md5 = MD5Builder();
 
     if(size == 0) {
         _error = UPDATE_ERROR_SIZE;