Include nvs_commit() on three methods (#5309)

* Include nvs_commit() on three methods

In [Preferences.cpp](https://github.com/espressif/arduino-esp32/blob/master/libraries/Preferences/src/Preferences.cpp),  the functions:
```
Preferences::clear()
Preferences::remove()
Preferences::end()
```
should be revised to include a call to 
`nvs_commit()`
as required per 
[Non-volatile storage library](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/storage/nvs_flash.html)
when using 
```
nvs_erase_all()
nvs_erase_key()
nvs_close()
```

libraries/Preferences/src/Preferences.cpp

-// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
+// Copyright 2015-2021 Espressif Systems (Shanghai) PTE LTD
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
+
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
@@ -43,7 +44,7 @@ bool Preferences::begin(const char * name, bool readOnly, const char* partition_
         }
         err = nvs_open_from_partition(partition_label, name, readOnly ? NVS_READONLY : NVS_READWRITE, &_handle);
     } else {
-        err = nvs_open(name, readOnly?NVS_READONLY:NVS_READWRITE, &_handle);
+        err = nvs_open(name, readOnly ? NVS_READONLY : NVS_READWRITE, &_handle);
     }
     if(err){
         log_e("nvs_open failed: %s", nvs_error(err));
@@ -74,6 +75,11 @@ bool Preferences::clear(){
         log_e("nvs_erase_all fail: %s", nvs_error(err));
         return false;
     }
+    err = nvs_commit(_handle);
+    if(err){
+        log_e("nvs_commit fail: %s", nvs_error(err));
+        return false;
+    }
     return true;
 }
 
@@ -90,6 +96,11 @@ bool Preferences::remove(const char * key){
         log_e("nvs_erase_key fail: %s %s", key, nvs_error(err));
         return false;
     }
+    err = nvs_commit(_handle);
+    if(err){
+        log_e("nvs_commit fail: %s %s", key, nvs_error(err));
+        return false;
+    }
     return true;
 }