fix: promote abbreviation unit for negative numbers that round up

[spokodev]

Problem

When a negative value rounds up to the next abbreviation boundary, the formatter promotes the unit for positive numbers but not for negative ones, producing malformed output:

numeral(-999999).format('0a')      // actual "-1000k"   expected "-1m"
numeral(-999999999).format('0a')   // actual "-1000m"   expected "-1b"
numeral(-999999).format('0.0a')    // actual "-1000.0k" expected "-1.0m"

The positive mirrors already format correctly, and the existing test data asserts that promotion:

[999999999,'0a','1b'],
[999950,'0.0a','1.0m'],

Only the negative side was never covered.

Root cause

The post-rounding promotion guard in numeral._.numberToFormat compares the signed value:

if (abbr && !abbrForce && Number(int) >= 1000 && abbr !== locale.abbreviations.trillion) {

For a value like -999999, after rounding int === "-1000", so Number(int) >= 1000 is false (signed comparison) and the unit promotion is skipped. The number is still divided down to -1 elsewhere, leaving the now-incorrect k suffix.

Fix

Compare the magnitude instead, restoring symmetry with the positive path:

if (abbr && !abbrForce && Math.abs(Number(int)) >= 1000 && abbr !== locale.abbreviations.trillion) {

Verification

• Added negative cases to the abbreviation test data (tests/numeral.js). They fail before the change (expected '-1000k' to equal '-1m') and pass after.
• Applied the change to src/numeral.js; the built numeral.js was regenerated via grunt build.
• Full Node suite green (grunt test:npm), including the existing positive abbreviation, spaced (0 a), and forced-abbreviation (0,0 ak/am/ab/at) cases.