fix parameter error in tutorial

[RenShuhuai-Andy]

In tutorial, some parameters of class mz.dataloader.Dataset are mistakenly placed in class mz.dataloader.DataLoader.

[codecov[bot]]

Codecov Report

Merging #124 into master will decrease coverage by 1.94%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #124      +/-   ##
==========================================
- Coverage   95.01%   93.07%   -1.95%     
==========================================
  Files         104      104              
  Lines        3811     3811              
==========================================
- Hits         3621     3547      -74     
- Misses        190      264      +74

Impacted Files	Coverage Δ
matchzoo/datasets/snli/load_data.py	26.47% <0%> (-70.59%)	:arrow_down:
matchzoo/datasets/wiki_qa/load_data.py	27.77% <0%> (-69.45%)	:arrow_down:
matchzoo/datasets/quora_qp/load_data.py	33.33% <0%> (-66.67%)	:arrow_down:
matchzoo/utils/get_file.py	73.14% <0%> (-4%)	:arrow_down:

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