doc/effective_go.html: fix typo Prose referred to 'b', code used 'buf'. Fixes issue 7601.
doc/effective_go.html: fix typo
Prose referred to 'b', code used 'buf'.
Fixes issue 7601.

LGTM=dominik.honnef
R=golang-codereviews, dominik.honnef
CC=golang-codereviews
https://codereview.appspot.com/78470043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang