fix: don't throw errors when there are multiple GOPATHs (#158)

This adds support for multiple entries in the GOPATH variable, which has the benefit that downloaded packages are placed in the path of the first entry of GOPATH while own packages can be managed in the second path.

functions/__sf_section_golang.fish

@@ -32,7 +32,7 @@ function __sf_section_golang -d "Display the current go version if you're inside
 		-o (count *.go) -gt 0 \
 		-o -f Gopkg.yml \
 		-o -f Gopkg.lock \
-		-o ([ -n $GOPATH ]; and string match $GOPATH $PWD)
+		-o ([ (count $GOPATH) -gt 0 ]; and string match $GOPATH $PWD)
 		return
 	end