Fix warning due to string literal in condition (#91)

Author: russell

ruby/private/binary_wrapper.tpl

@@ -119,8 +119,8 @@ def main(args)
   runfiles_envkey, runfiles_envvalue = runfiles_envvar(runfiles)
   ENV[runfiles_envkey] = runfiles_envvalue if runfiles_envkey
 
-  ENV["GEM_PATH"] = File.join(runfiles, "{gem_path}") if "{gem_path}"
-  ENV["GEM_HOME"] = File.join(runfiles, "{gem_path}") if "{gem_path}"
+  ENV["GEM_PATH"] = File.join(runfiles, "{gem_path}") if !"{gem_path}".empty?
+  ENV["GEM_HOME"] = File.join(runfiles, "{gem_path}") if !"{gem_path}".empty?
 
   ruby_program = find_ruby_binary