Fix usage of the word "verticies" to "vertices"

[ear7h]

To apply this change (to any code base), one line of bash can be used:

sed  -e 's/\([Vv]\)erticies/\1ertices/g' -i '' $(grep -e '[Vv]erticies' -r . -l --exclude='./.git/*')

closes #44

[coveralls]

Pull Request Test Coverage Report for Build 437

• 12 of 17 (70.59%) changed or added relevant lines in 10 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 57.538%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
encoding/wkt/wkt_encode.go	0	1	0.0%
geom.go	4	5	80.0%
line.go	0	1	0.0%
planar/clip/linestring.go	0	1	0.0%
planar/simplify.go	0	1	0.0%

Totals
Change from base Build 431:	0.4%
Covered Lines:	28366
Relevant Lines:	49300

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💛 - Coveralls

[gdey]

LGTM