Don't open subprocess as shell

That doesn't work when working as an unpacked plug-in in Cura.

X3GWriter.py

@@ -66,7 +66,7 @@ def write(self, stream, nodes, mode = MeshWriter.OutputMode.TextMode):
         Logger.log("d", "Command: %s", str(command))
         stream.close() #Close the file so that the binary can write to it.
         try:
-            process = subprocess.Popen(safes, shell=True)
+            process = subprocess.Popen(safes)
             process.wait()
             output = process.communicate(b"y")
             Logger.log("d", str(output))
@@ -86,4 +86,4 @@ def _removeTemporary(temp_file):
     try:
         os.remove(temp_file)
     except:
-        Logger.log("w", "Couldn't remove temporary file %s", temp_file)
+        Logger.log("w", "Couldn't remove temporary file %s", temp_file)