requirements: reword error messages for consistency

...ebrew/extend/os/linux/requirements/osxfuse_requirement.rb

...omebrew/extend/os/mac/requirements/osxfuse_requirement.rb

...ry/Homebrew/extend/os/mac/requirements/x11_requirement.rb

Library/Homebrew/requirement.rb

Library/Homebrew/requirements/arch_requirement.rb

Library/Homebrew/requirements/java_requirement.rb

Library/Homebrew/requirements/linux_requirement.rb

Library/Homebrew/requirements/macos_requirement.rb

Library/Homebrew/requirements/x11_requirement.rb

Library/Homebrew/test/java_requirement_spec.rb

...ry/Homebrew/test/requirements/osxfuse_requirement_spec.rb