apply str.strip() in sanitize_date

[noviluni]

The trailing spaces can cause unexpected issues. For example:

>>> dateparser.parse('Mon, 25 Jun 2018 10:37:47 +0530 ')

returns None.

(Or this: #691).

For that reason, I added an str.strip() to the sanitize_date() function.

[codecov]

Codecov Report

Merging #841 (25ed605) into master (939e722) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #841      +/-   ##
==========================================
+ Coverage   98.33%   98.37%   +0.03%     
==========================================
  Files         231      231              
  Lines        2590     2591       +1     
==========================================
+ Hits         2547     2549       +2     
+ Misses         43       42       -1     

Impacted Files	Coverage Δ
dateparser/date.py	100.00% <100.00%> (ø)
dateparser/languages/dictionary.py	100.00% <0.00%> (+0.67%)	⬆️

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