Added AST node type NoAliasAttr. Fixes #769

[kamphaus]

Fixes #769

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This change is 

[codecov]

Codecov Report

Merging #770 into master will decrease coverage by 0.06%.
The diff coverage is 52.38%.

@@            Coverage Diff             @@
##           master     #770      +/-   ##
==========================================
- Coverage   80.69%   80.63%   -0.07%     
==========================================
  Files         166      167       +1     
  Lines        9485     9506      +21     
==========================================
+ Hits         7654     7665      +11     
- Misses       1398     1408      +10     
  Partials      433      433

Impacted Files	Coverage Δ
ast/position.go	79.09% <0%> (-0.52%)	⬇️
ast/ast.go	98.31% <100%> (+0.01%)	⬆️
ast/no_alias_attr.go	52.94% <52.94%> (ø)

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[elliotchance]

Reviewed 4 of 4 files at r1.
Review status: complete! all files reviewed, all discussions resolved

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