fix dynamic attribute priority

[mlrawlings]

Description

No matter where the dynamic ${attrs} are defined, they always have lowest priority. In the following example, both explicit foo and bar attributes would overwrite any values in attrs.

<div foo=123 ${attrs} bar=456>Hello World</div>

The current migration gives highest priority to these dynamic attributes rather than lowest.

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1223 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1223      +/-   ##
==========================================
+ Coverage   90.57%   90.58%   +<.01%     
==========================================
  Files         333      334       +1     
  Lines       12235    12244       +9     
==========================================
+ Hits        11082    11091       +9     
  Misses       1153     1153

Impacted Files	Coverage Δ
src/taglibs/migrate/all-tags/dynamic-attributes.js	100% <100%> (ø)	⬆️
src/taglibs/migrate/all-tags/widget-elId.js	100% <0%> (ø)

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[coveralls]

Coverage increased (+0.0008%) to 90.577% when pulling 3bd5fa8 on dynamic-attribute-priority into aef04be on master.