ignore the nil core module config args. such as: passenger

when install  `brew install nginx-full --with-passenger`
it will raise `./configure: error: invalid option "--with-"`

because the configure args not ignore nil value
~~~ruby
args += self.class.core_modules.select { |arr|
  build.with? arr[0]
}.collect { |arr|
  "--with-#{arr[1]}"
}
~~~

should be change to
~~~ruby
args += self.class.core_modules.select { |arr|
  build.with? arr[0]
}.collect { |arr|
  "--with-#{arr[1]}" if arr[1]
}.compact
~~~