refactor(README.md): change Latex link from pygments to lstlean
refactor(README.md): change Latex link from pygments to lstlean

fpvandoorn/lean2,fpvandoorn/lean2,soonhokong/lean,soonhokong/lean,javra/lean,soonhokong/lean,fpvandoorn/lean2,UlrikBuchholtz/lean,soonhokong/lean,UlrikBuchholtz/lean,UlrikBuchholtz/lean,javra/lean,javra/lean,javra/lean,javra/lean,fpvandoorn/lean2,soonhokong/lean,fpvandoorn/lean2,UlrikBuchholtz/lean,UlrikBuchholtz/lean