Correctly convert RestProperty to Assignable

[danez]

Q	A
Bug fix?	yes
Breaking change?	no
New feature?	no
Deprecations?	no
Spec compliancy?	yes
Tests added/pass?	yes
Fixed tickets	Fixes #304 Fixes #309
License	MIT

if the parsed spread is inside of an ObjectPattern we need to convert it to an assignable (ObjectExpression->ObjectPattern).
Also when parsing the spread inside a ObjectPattern we need to allow shorthand properties.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@407c97c). Click here to learn what that means.

@@            Coverage Diff            @@
##             master     #339   +/-   ##
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  Coverage          ?   97.65%           
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  Files             ?       20           
  Lines             ?     3327           
  Branches          ?      884           
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  Hits              ?     3249           
  Misses            ?       30           
  Partials          ?       48

Impacted Files	Coverage Δ
src/parser/expression.js	97.33% <100%> (ø)

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