cmd/go/internal/load: fix IsMetaPackage function name in doc

The IsMetaPackage function was made exported when it was moved from
cmd/go to cmd/go/internal/load in CL 36196. Its documentation wasn't
updated accordingly. This change fixes that, resolving a golint issue.

Updates #18653.

Change-Id: Icf89461000754d0f09e6617b11c838e4c050d5a6
Reviewed-on: https://go-review.googlesource.com/59430Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/go/internal/load/search.go

@@ -332,7 +332,7 @@ func ImportPathsNoDotExpansion(args []string) []string {
 	return out
 }
 
-// isMetaPackage checks if name is a reserved package name that expands to multiple packages.
+// IsMetaPackage checks if name is a reserved package name that expands to multiple packages.
 func IsMetaPackage(name string) bool {
 	return name == "std" || name == "cmd" || name == "all"
 }