Fix typo in the Accumulators section

val => var
Merge pull request #310 from jyunfan/master

Fix typo in the Accumulators section

Change 'val' to 'var'
Revert "Merge pull request #310 from jyunfan/master"

This reverts commit 79b20e4dbe3dcd8559ec8316784d3334bb55868b, reversing
changes made to 7375047d516c5aa69221611f5f7b0f1d367039af.