Give NLog output file a better name

Author: Caitlin Bales (MSFT)

src/GraphODataTemplateWriter/NLog.config

@@ -16,7 +16,7 @@
   for information on customizing logging rules and outputs.
    -->
   <targets>
-    <target name="logfile" xsi:type="File" fileName="file.txt" />
+    <target name="logfile" xsi:type="File" fileName="generator-output.txt" />
     <!--
     add your targets here
     See https://github.com/nlog/NLog/wiki/Targets for possible targets.