fix: deprecated ci action and minor typo

Signed-off-by: Luca Marchiori <luca.marchiori@secomind.com>

Author: lucamarchiori

.github/workflows/main.yml

@@ -42,7 +42,7 @@ jobs:
 
     # Load artifacts obtained with the most recent version of Go
     - name: Upload build artifacts
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       if: matrix.go == '1.20.x'
       with:
         path: astartectl*

README.md

@@ -72,12 +72,12 @@ Generally speaking, one of those could be written like
 ```
 or, for aggregated interfaces, like a json object:
 ```
- astartectl appengine devices publish-datastream 2TBn-jNESuuHamE2Zo1anA com.my.interface.aggregated /my/path  '{"path1": "value2","path2":"value2"}'
+ astartectl appengine devices publish-datastream 2TBn-jNESuuHamE2Zo1anA com.my.interface.aggregated /my/path  '{"path1":"value1","path2":"value2"}'
 ```
 
 Please note, "value" is whatever your raw value is, no encapsulation whatsoever is required by astarte or astartectl (but you can provide your own, if you need it). 
 Exceptions follow:
 - arrays are written like ["value", "anothervalue"] (depending on your shell, this can also be "['value', 'anothervalue']", please check before using in a production env)
 - aggregates values could be anything accepted by astarte, in case of arrays they follow the above rule
 - binaryblobs must be base64 encoded
-- datetime is based on an external library that is flexible enough to translate a fairly high number of different formats, further documentation and supported formats can be found [here](https://github.com/araddon/dateparse)
+- datetime is based on an external library that is flexible enough to translate a fairly high number of different formats, further documentation and supported formats can be found [here](https://github.com/araddon/dateparse)