Hiring by America’s employers picked up a bit in August from July’s tepid pace, and the unemployment rate dipped for the first time since March in a sign that the job market may be cooling but remains sturdy. Employers added a modest 142,000 jobs, up from a scant 89,000 in July. The unemployment rate ticked down to 4.2% from 4.3% in July, which had been the highest level in nearly three years. Hiring in June and July, though, was revised sharply down. The cooling jobs figures underscore why the Federal Reserve is set to cut its key interest rate when it next meets Sept. 17-18, with inflation falling steadily back to its target of 2%.