Update 2013-07-10-design-patterns-template-pattern.md

changed ConcreteWall material to concrete, WoodWall material to wood. Changed 'could of' to 'could have'. 'Could of' is a mispronunciation of 'could've'.
Merge pull request #60 from marc-fez/patch-1

Update 2013-07-10-design-patterns-template-pattern.md