Make shfmt happy

(I'm open to better ways of formatting the heredoc
that embeds the Python script.)

notify/smtp.sh

@@ -125,7 +125,8 @@ _smtp_send() {
   fi
 
   # language=Python
-  smtp_send_output="$($SMTP_PYTHON <<EOF
+  smtp_send_output="$(
+    $SMTP_PYTHON <<EOF
 # This code is meant to work with either Python 2.7.x or Python 3.4+.
 try:
     try: