doc/effective_go: minor fix

        We have 'gofmt' and 'go fmt', but not 'go tool fmt'.

R=golang-dev, kyle, r
CC=golang-dev
https://golang.org/cl/5739043

doc/effective_go.html

@@ -69,7 +69,7 @@ With Go we take an unusual
 approach and let the machine
 take care of most formatting issues.
 The <code>gofmt</code> program
-(also available as <code>go tool fmt</code>, which
+(also available as <code>go fmt</code>, which
 operates at the package level rather than source file level)
 reads a Go program
 and emits the source in a standard style of indentation

doc/effective_go.tmpl

@@ -65,7 +65,7 @@ With Go we take an unusual
 approach and let the machine
 take care of most formatting issues.
 The <code>gofmt</code> program
-(also available as <code>go tool fmt</code>, which
+(also available as <code>go fmt</code>, which
 operates at the package level rather than source file level)
 reads a Go program
 and emits the source in a standard style of indentation