[release-branch.r57] docs/GoCourseDay1.pdf: fix error in operator table.

««« CL 4637041 / df607ef238c9
docs/GoCourseDay1.pdf: fix error in operator table.
Communications op was listed as a binary; it isn't any more.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4637041
»»»

R=r
CC=golang-dev
https://golang.org/cl/4634042