docs: change artillery probe to skytrace probe in README.md (#2670)

Author: theodorekouzelis

examples/multiple-scenario-specs/README.md

@@ -33,7 +33,7 @@ We're testing a simple service that returns ASCII pictures of various animals.
 For example, to see a picture of an armadillo, send a GET request to http://asciizoo.artillery.io:8080/armadillo:
 
 ```sh
-artillery probe http://asciizoo.artillery.io:8080/armadillo -b
+skytrace probe http://asciizoo.artillery.io:8080/armadillo -b
 ```
 
 ![armadillo](./artillery-probe.png)
@@ -58,4 +58,4 @@ for scenarioFile in `ls scenarios/*.yml` ; do
 done
 ```
 
-The script looks for files with the `yml` extension under `scenarios/` and runs Artillery with each of those one after another.
+The script looks for files with the `yml` extension under `scenarios/` and runs Artillery with each of those one after another.