webapp: use shell=True in autocompile script

we need shell=True as on Windows, path resolution to find the yarn
"exectuable" (a shell script) is only performed by cmd.exe, not by
Python itself. as we are calling yarn with fixed arguments, using
shell=True is fine.

pio-scripts/compile_webapp.py

@@ -33,22 +33,26 @@ def check_files(directories, filepaths, hash_file):
 
     print("INFO: compiling webapp (hang on, this can take a while and there might be little output)...")
 
+    # we need shell=True as on Windows, path resolution to find the yarn
+    # "exectuable" (a shell script) is only performed by cmd.exe, not by
+    # Python itself. as we are calling yarn with fixed arguments, using
+    # shell=True is fine.
     yarn = "yarn"
     try:
-        subprocess.check_output([yarn, "--version"])
+        subprocess.check_output([yarn, "--version"], shell=True)
     except FileNotFoundError:
         yarn = "yarnpkg"
         try:
-            subprocess.check_output([yarn, "--version"])
+            subprocess.check_output([yarn, "--version"], shell=True)
         except FileNotFoundError:
             raise Exception("it seems neither 'yarn' nor 'yarnpkg' is installed/available on your system")
 
     # if these commands fail, an exception will prevent us from
     # persisting the current hashes => commands will be executed again
     subprocess.run([yarn, "--cwd", "webapp", "install", "--frozen-lockfile"],
-                   check=True)
+                   check=True, shell=True)
 
-    subprocess.run([yarn, "--cwd", "webapp", "build"], check=True)
+    subprocess.run([yarn, "--cwd", "webapp", "build"], check=True, shell=True)
 
     with open(hash_file, 'wb') as f:
         pickle.dump(file_hashes, f)