Fix parsing of tag in find feature to consider whitespaces

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files with missing lines	Coverage Δ	Complexity Δ
...in/java/seedu/address/logic/parser/ParserUtil.java	68.33% <100.00%> (ø)	17.00 <0.00> (ø)

[hansneddyanto]

Resolves #289