Disable copy button for bad pre blocks

docs/_posts/2009-10-06-edge-case-broken-highlighting.md

@@ -21,13 +21,28 @@ if str
 end
 ```
 
+Good (but dumb) highlighting:
+
+```
+str = ARGV.first
+if str
+  str = str.b[/\A_(.*)_\z/, 1]
+  if str and Gem::Version.correct?(str)
+    version = str
+    ARGV.shift
+  end
+end
+```
+
 Bad highlighting:
 
 ```invalid
-if Gem.respond_to?(:activate_bin_path)
-  load Gem.activate_bin_path('jekyll', 'jekyll', version)
-else
-  gem "jekyll", version
-  load Gem.bin_path("jekyll", "jekyll", version)
+str = ARGV.first
+if str
+  str = str.b[/\A_(.*)_\z/, 1]
+  if str and Gem::Version.correct?(str)
+    version = str
+    ARGV.shift
+  end
 end
 ```