fix reference link

[alecloudenback]

Simple fix for old docs link in README

[codecov]

Codecov Report

Merging #170 (00df0ab) into master (8cc2855) will increase coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
+ Coverage   96.94%   97.08%   +0.13%     
==========================================
  Files           7        7              
  Lines         885      959      +74     
==========================================
+ Hits          858      931      +73     
- Misses         27       28       +1     

Impacted Files	Coverage Δ
src/error.jl	94.28% <0.00%> (-2.59%)	⬇️
src/buffer.jl	100.00% <0.00%> (ø)
src/node.jl	99.01% <0.00%> (+0.07%)	⬆️
src/document.jl	95.83% <0.00%> (+0.10%)	⬆️
src/xpath.jl	96.29% <0.00%> (+0.29%)	⬆️
src/streamreader.jl	93.47% <0.00%> (+1.12%)	⬆️

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