It's usually because someone copied and pasted on Windows. Go expects UTF-8 encoded source files.
What is output from:
go version
Did you follow the instructions for downloading the source files for the book?
Programming in Go
http://www.qtrac.eu/gobook.htmlDownloads
The source code is available in two formats, gobook-1.0.tar.gz[
http://www.qtrac.eu/gobook-1.0.tar.gz] (70K suitable for any platform), and gobook-1.0.zip[
http://www.qtrac.eu/gobook-1.0.zip] (170K Windows line endings) [updated 2013-10-09] and have been tested with Go 1.0, Go 1.1, and Go 1.2—they are subject to the very liberal Apache 2.0 license. There is also an Errata [updated 2013-06-28].
Peter