code: function getRelevantCombinations( wordCombinations ) {
  	wordCombinations = wordCombinations.filter( function( combination ) {
  		return combination.getOccurrences() !== 1 &&
  			combination.getRelevance() !== 0;
  	} );
  	return wordCombinations;
  }
docs: Returns only the relevant combinations from a list of word combinations. Assumes
  occurrences have already been calculated.
  
  @param {WordCombination[]} wordCombinations A list of word combinations.
  @returns {WordCombination[]} Only relevant word combinations.