Replace use of master in Windows Dockerfile
The `master` alias for the `aggregator` command was removed in
however this alias was still in use in the Windows Dockerfile. Replace
the use of this with the new command name `aggregator`.
@@ -17,4 +17,4 @@ MAINTAINER John Schnake "jschnake@vmware.com"
ADD BINARY /sonobuoy.exe
WORKDIR /
-CMD /sonobuoy.exe master --no-exit -v 3 --logtostderr
\ No newline at end of file
+CMD /sonobuoy.exe aggregator --no-exit -v 3 --logtostderr
