Update base.rst to match currently available `quantile` methods

This edits help(quantile) and help(quantile!) to match up with methods(quantile) and methods(quantile!)

Current methods(quantile) output:
~~~jl
julia> methods(quantile)
# 2 methods for generic function "quantile":
quantile(v::AbstractArray{T,1},q::AbstractArray{T,1}) at statistics.jl:288
quantile(v::AbstractArray{T,1},q::Number) at statistics.jl:289

julia> methods(quantile!)
# 1 method for generic function "quantile!":
quantile!(v::AbstractArray{T,1},q::AbstractArray{T,1}) at statistics.jl:268
~~~

Github's online editing interface seems to be super-slow for editing when the file is as big as base.rst. =/