Fix openssl-dir param

Author: Kimmo Lehto

bin/rubyc

@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 
 # Copyright (c) 2017 Minqi Pan <[email protected]>
-# 
+#
 # This file is part of Ruby Compiler, distributed under the MIT License
 # For full terms see the included LICENSE file
 
@@ -29,13 +29,13 @@ Examples
   Producing a single Ruby interpreter executable:
     rubyc
     ./a.out (or a.exe on Windows)
-  
+
   Compiling a CLI tool:
     git clone --depth 1 https://github.com/pmq20/ruby-compiler.git
     cd ruby-compiler
     rubyc bin/rubyc
     ./a.out (or a.exe on Windows)
-  
+
   Compiling a Rails application:
     rails new yours
     cd yours
@@ -79,7 +79,7 @@ OptionParser.new do |opts|
     options[:keep_tmpdir] = true
   end
 
-  opts.on("--openssl-dir", "The path to openssl") do |dir|
+  opts.on("--openssl-dir=DIR", "The path to openssl") do |dir|
     options[:openssl_dir] = dir
   end