bump DSP compat to 0.7; fix csv-to-matrix function to DataFrames 1

[kleinschmidt]

DSP 0.7 was released recently, with changes that don't affect the use of filt! here AFAIK.

This also fixes the function to convert a dataframe into a matrix since it was erroring with DataFrames 1.

[codecov-commenter]

Codecov Report

Merging #59 (d8f6985) into master (ea74151) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #59      +/-   ##
==========================================
+ Coverage   92.45%   92.52%   +0.06%     
==========================================
  Files           8        8              
  Lines        1114     1111       -3     
==========================================
- Hits         1030     1028       -2     
+ Misses         84       83       -1     

Impacted Files	Coverage Δ
src/Lasso.jl	90.69% <0.00%> (+0.27%)	⬆️

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[AsafManela]

Thank you!