Changed wording in assertions to sound better:

to not be -> not to be

to not be ok > not to be ok
to not be truthy -> not to be truthy

to not be a -> not to be a
to not be an -> not to be an
to not be a boolean -> not to be a boolean
to not be a number -> not to be a number
to not be a string -> not to be a string
to not be a function -> not to be a function
to not be an object -> not to be an object
to not be an array -> not to be an array
to not be a regexp -> not to be a regexp
to not be a regex -> not to be a regex
to not be a regular -> not to be a regular
to not be an expression -> not to be an expression

to not match -> not to match

to not have property -> not to have property
to not have own property -> not to have own property

to not have length -> not to have length

to not be empty -> not to be empty

to not have key -> not to have key
to not have keys -> not to have keys

to not contain -> not to contain

to not be within -> not to be within

to not equal -> not to equal

to not throw -> not to throw

I desided to make this very breaking change after a long conversation with @papandreou - I guess it is better to break things now compared to later.
1.0.0