Note that by Taylor's expansions
* $\log (1+x)=x+o(x)$
* $e^x=1+x+o(x)$
we have
$$(1+x)^x=e^{x\log(1+x)}=e^{x^2+o(x^2)}=1+x^2+o(x^2)$$
thus
$$[(x+1)^x-1] ^x=[1+x^2+o(x^2)-1] ^x=(x^2+o(x^2))^x=e^{x(\log x^2+o(x^2))}\to 1$$
indeed
$$x[\log x^2+o(x^2)]=x[\log x^2+\log (1+o(1))]=2x\log x+x\log(1+o(1))\to0+0=0$$