Escape issue search string

Fixes Homebrew/homebrew#25779.

Library/Homebrew/utils.rb

@@ -277,10 +277,19 @@ module GitHub extend self
   end
 
   def each_issue_matching(query, &block)
-    uri = ISSUES_URI + query
+    uri = ISSUES_URI + uri_escape(query)
     open(uri) { |f| Utils::JSON.load(f.read)['issues'].each(&block) }
   end
 
+  def uri_escape(query)
+    if URI.respond_to?(:encode_www_form_component)
+      URI.encode_www_form_component(query)
+    else
+      require "erb"
+      ERB::Util.url_encode(query)
+    end
+  end
+
   def issues_for_formula name
     # bit basic as depends on the issue at github having the exact name of the
     # formula in it. Which for stuff like objective-caml is unlikely. So we