OT (sort of): VIM/ex/tr question

[John P. Verel]

Greetings.

I have a vim file which, in general, resembles this:
                Hello
world
                Hello
world

I want to concatenate Hello and world.  fmt won't do because Hello ends with a
newline character.

I've tried the following (in vim 5.7), which does not work:

:g/\s*/!!tr '\n' ' '

The ex global command locates the lines with the white space, but the tr
command won't translate the newline to a space.  The man page for tr shows \n
as the special character for a newline.

Any thoughts?

TIA

John