add parameter to handle svg aspect ratio

[aguerot]

In some case it is interesting to be able to control svg aspect ratio
Using ngx-trend as such:
<ngx-trend autoDraw="true" autoDrawDuration="3000" autoDrawEasing="ease-out" smooth="true" preserveAspectRatio="none" height="100" [data]="placeholderData" [gradient]="gradient" [radius]="radius" [strokeWidth]="strokeWidth"[strokeLinecap]="strokeLinecap">
allows to address some scenarios where the default 1:4 ratio would not fit in wide screen

[codecov-io]

Codecov Report

Merging #97 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
+ Coverage   94.02%   94.05%   +0.03%     
==========================================
  Files          15       15              
  Lines         184      185       +1     
  Branches       22       22              
==========================================
+ Hits          173      174       +1     
  Misses          6        6              
  Partials        5        5

Impacted Files	Coverage Δ
src/lib/trend/trend.component.ts	98.11% <100%> (+0.03%)	⬆️

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