Keep space before word after inserting completion

[evidolob]

What does this PR do?

When completion invoked on field which has value:
name: <cursor>aName and file has scheme which contains defaultSnippets for name:

"properties": {
      "name": {
          "type": "string",
          "defaultSnippets": [
              {
                  "label": "some",
                  "body": "some"
              }
          ]
      },
}

it contains one option some, but inserting of that item will break yaml, as it 'eats' space after ::
name:someaName, this PR fix that, and now it no break yaml, so editor should contain name: someaName.

What issues does this PR fix or reference?

Found during work on redhat-developer/vscode-tekton#429

Is it tested? How?

You may use schema example from this description, or try complete any yaml mapping value. Completion shouldn't breck yaml syntax.

[coveralls]

Coverage decreased (-0.2%) to 80.061% when pulling 53b10c9 on evidolob:fix-insertion into ce1609d on redhat-developer:master.

[JPinkney]

The test case worked for me. I just found out we have another semi-related issue that is present on master as well though

If we have an empty document and then auto complete at the root with the schema given we will get:

name:some

instead of

name: some

It's unrelated to this PR but I found it while testing 😄. I'll open an issue for it

EDIT: The issue is here: #364