Suppress warnings

Suppress following warnings when 'rake'

    lib/epub.rb:9: warning: `*' interpreted as argument prefix
    lib/epub.rb:50: warning: `&' interpreted as argument prefix
    lib/epub.rb:68: warning: `&' interpreted as argument prefix
    lib/epub/parser/publication.rb:214: warning: ambiguous first argument; put parentheses or even spaces
    lib/epub/parser/publication.rb:216: warning: ambiguous first argument; put parentheses or even spaces
    lib/epub/parser/publication.rb:223: warning: ambiguous first argument; put parentheses or even spaces
    lib/epub/publication/package.rb:30: warning: `*' interpreted as argument prefix
    lib/epub/publication/package/metadata.rb:58: warning: possibly useless use of +@ in void context
    test/test_inspect.rb:40: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:68: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:69: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:70: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:71: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:80: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:88: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:89: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:90: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:91: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:105: warning: ambiguous first argument; put parentheses or even spaces
    test/test_inspect.rb:116: warning: ambiguous first argument; put parentheses or even spaces

but, following warnings are not fixed

    lib/epub/publication/package/guide.rb:22: warning: instance variable @cover not initialized
    lib/epub/publication/package/guide.rb:35: warning: instance variable @item not initialized