[GSoC] Fix state space of Wiener Process

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[Smit-create]

@czgdp1807 Please merge this when the tests pass

[Smit-create]

Failing job on Travis: https://travis-ci.org/github/sympy/sympy/jobs/716238524

[codecov]

Codecov Report

Merging #19926 into master will increase coverage by 11.535%.
The diff coverage is 100.000%.

@@              Coverage Diff               @@
##            master    #19926        +/-   ##
==============================================
+ Coverage   64.256%   75.792%   +11.535%     
==============================================
  Files          666       668         +2     
  Lines       172568    173188       +620     
  Branches     40689     40842       +153     
==============================================
+ Hits        110887    131263     +20376     
+ Misses       55277     36197     -19080     
+ Partials      6404      5728       -676