Define MulStyle(::ScaledMap) in terms of wrapped map

[dkarrasch]

Closes #178.

[codecov]

Codecov Report

Merging #179 (7f77927) into master (aa54eb3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #179   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files          14       14           
  Lines        1150     1151    +1     
=======================================
+ Hits         1146     1147    +1     
  Misses          4        4           

Impacted Files	Coverage Δ
src/scaledmap.jl	100.00% <100.00%> (ø)

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