Use utf-8 so we support non-ascii module names

It's safe to assume that this is always utf-8-safe because we only ever use the function to send Python source code, which must be utf-8 encodable (and indeed utf-8 at rest)

Author: Zac-HD

execnet/gateway_bootstrap.py

@@ -75,7 +75,7 @@ def bootstrap_socket(io, id):
 
 def sendexec(io, *sources):
     source = "\n".join(sources)
-    io.write((repr(source) + "\n").encode("ascii"))
+    io.write((repr(source) + "\n").encode("utf-8"))
 
 
 def fix_pid_for_jython_popen(gw):