Which is more stable out of the given carbocation? Which is more stable?

$\ce{^+C(CH3)3}$
$\ce{^+C(CD3)3}$


I have read in Solomon's and Fryhle that the +I effect of D is more than that of H but here in this problem it is given that $\ce{(CH3)3C+}$ is more stable.
How is this possible? Since, deuterium enriches the electron density over the central carbon resulting in the diminishing of a positive charge eventually making the second structure more stable.
Second explanation can be on the basis of hyperconjugation which says that $\ce{-CH3}$ is better in showing hyperconjugation than $\ce{-CD3}$, but why is this so?
$\ce{C-D}$ bonds are stronger. Hyperconjugation is thus more easily seen  with hydrogen rather than deuterium.   Hyperconjugation> Inductive effects at stabilization.I believe you can reason the rest out by yourself.  To see why $\ce{C-D}$ bonds are stronger. 

See this