Fixed no escaped space bug(53af9a6)

    describe file("/home") do
        it { should be_mounted }
    end
------------------------------------
    Failures:
    1) マウント File "/home" should be mounted
         On host ``
         Failure/Error: it { should be_mounted }
           mount | grep -w -- on\ /home\
           expected File "/home" to be mounted


I have error above in the 53af9a6 commit.
I think grep command does not require the -w option. and need to escape the comma for regexp.