Align gutter width with old compiler

[haoqixu]

tsc 5.8.2:

Before:

After:

[haoqixu]

ref: https://github.com/microsoft/TypeScript/blob/release-3.9/src/compiler/program.ts#L390

[jakebailey]

For reference, the original code is:

    const hasMoreThanFiveLines = (lastLine - firstLine) >= 4;
    let gutterWidth = (lastLine + 1 + "").length;
    if (hasMoreThanFiveLines) {
        gutterWidth = Math.max(ellipsis.length, gutterWidth);
    }

So your fix is definitely correct; the + "" was a conversion.