Options on new lines don't get scoped as options

[alexr00]

The code with a problem is:

# good
ls -alh

# good
ls \
    -alh \

# not good, `-alh` should be "blue" as well
ls \
-alh \

It looks like:

It should look like:

The -alh options should have the same scopes and color in all three examples.

The correct -alh tokens have the following scopes:

constant.other.option.dash.shell
string.unquoted.argument.shell
meta.statement.command.shell
meta.statement.shell
source.shell

The incorrect one has:

meta.statement.command.shell
meta.statement.shell
source.shell

Originally from @liufeimath in microsoft/vscode#225561