Fix wrong picker marker (a typo during lab 4.0 migration)

[krassowski]

This is a follow-up to #673, something I noticed when looking into #676

For reference, this is the corresponding code on 3.2 branch:

nbdime/packages/nbdime/src/common/mergeview.ts

Lines 555 to 572 in 1b368a8

	// When the chunk is empty, make sure a horizontal line shows up
	if (from === to) {
	let line = editor.addLineClass(from, 'background', classes.start);
	if (self.type !== 'merge') {
	let picker = elt('div', PICKER_SYMBOL, classes.gutter);
	(picker as any).sources = sources;
	picker.classList.add(GUTTER_PICKER_CLASS);
	editor.setGutterMarker(line, GUTTER_PICKER_CLASS, picker);
	} else if (conflict) {
	// Add conflict markers on editor, if conflicted
	let conflictMarker = elt('div', CONFLICT_MARKER, '');
	(conflictMarker as any).sources = sources;
	conflictMarker.classList.add(GUTTER_CONFLICT_CLASS);
	editor.setGutterMarker(line, GUTTER_CONFLICT_CLASS, conflictMarker);
	}
	editor.addLineClass(line, 'background', classes.end + '-empty');
	markers.push(line);
	}

it was also using conflict so I assume picker here on the master branch is a typo.

[HaudinFlorence]

@krassowski Thanks for pointing this wrong picker marker. This seems to be an error or a copy paste reminiscence.