Fix for ascii equivalent for greek letter theta

This is a fix for the Greek letter Theta (https://en.wikipedia.org/wiki/Theta) which is now replaced by O which is completely irrelevant.
I believe this was a mistake in the original code due to the cyrilic ө (https://en.wiktionary.org/wiki/%D3%A8) which is correctly replaced by ο (it is left untouched in my proposal).

I have also created a PR to the original source danielstjules/Stringy#193 but the project seems abandonded. However my changes were copied on a better mantained fork https://github.com/voku/Stringy

P.S. I am a Greek native speaker

Author: nikosv

Str.php

@@ -632,7 +632,7 @@ protected static function charsArray()
             'l'    => ['ł', 'ľ', 'ĺ', 'ļ', 'ŀ', 'л', 'λ', 'ل', 'လ', 'ლ', 'ｌ'],
             'm'    => ['м', 'μ', 'م', 'မ', 'მ', 'ｍ'],
             'n'    => ['ñ', 'ń', 'ň', 'ņ', 'ʼn', 'ŋ', 'ν', 'н', 'ن', 'န', 'ნ', 'ｎ'],
-            'o'    => ['ó', 'ò', 'ỏ', 'õ', 'ọ', 'ô', 'ố', 'ồ', 'ổ', 'ỗ', 'ộ', 'ơ', 'ớ', 'ờ', 'ở', 'ỡ', 'ợ', 'ø', 'ō', 'ő', 'ŏ', 'ο', 'ὀ', 'ὁ', 'ὂ', 'ὃ', 'ὄ', 'ὅ', 'ὸ', 'ό', 'о', 'و', 'θ', 'ို', 'ǒ', 'ǿ', 'º', 'ო', 'ओ', 'ｏ', 'ö'],
+            'o'    => ['ó', 'ò', 'ỏ', 'õ', 'ọ', 'ô', 'ố', 'ồ', 'ổ', 'ỗ', 'ộ', 'ơ', 'ớ', 'ờ', 'ở', 'ỡ', 'ợ', 'ø', 'ō', 'ő', 'ŏ', 'ο', 'ὀ', 'ὁ', 'ὂ', 'ὃ', 'ὄ', 'ὅ', 'ὸ', 'ό', 'о', 'و', 'ို', 'ǒ', 'ǿ', 'º', 'ო', 'ओ', 'ｏ', 'ö'],
             'p'    => ['п', 'π', 'ပ', 'პ', 'پ', 'ｐ'],
             'q'    => ['ყ', 'ｑ'],
             'r'    => ['ŕ', 'ř', 'ŗ', 'р', 'ρ', 'ر', 'რ', 'ｒ'],
@@ -665,7 +665,7 @@ protected static function charsArray()
             'shch' => ['щ'],
             'ss'   => ['ß'],
             'sx'   => ['ŝ'],
-            'th'   => ['þ', 'ϑ', 'ث', 'ذ', 'ظ'],
+            'th'   => ['þ', 'ϑ', 'θ', 'ث', 'ذ', 'ظ'],
             'ts'   => ['ц', 'ც', 'წ'],
             'ue'   => ['ü'],
             'uu'   => ['ऊ'],
@@ -687,7 +687,7 @@ protected static function charsArray()
             'L'    => ['Ĺ', 'Ł', 'Л', 'Λ', 'Ļ', 'Ľ', 'Ŀ', 'ल', 'Ｌ'],
             'M'    => ['М', 'Μ', 'Ｍ'],
             'N'    => ['Ń', 'Ñ', 'Ň', 'Ņ', 'Ŋ', 'Н', 'Ν', 'Ｎ'],
-            'O'    => ['Ó', 'Ò', 'Ỏ', 'Õ', 'Ọ', 'Ô', 'Ố', 'Ồ', 'Ổ', 'Ỗ', 'Ộ', 'Ơ', 'Ớ', 'Ờ', 'Ở', 'Ỡ', 'Ợ', 'Ø', 'Ō', 'Ő', 'Ŏ', 'Ο', 'Ό', 'Ὀ', 'Ὁ', 'Ὂ', 'Ὃ', 'Ὄ', 'Ὅ', 'Ὸ', 'Ό', 'О', 'Θ', 'Ө', 'Ǒ', 'Ǿ', 'Ｏ', 'Ö'],
+            'O'    => ['Ó', 'Ò', 'Ỏ', 'Õ', 'Ọ', 'Ô', 'Ố', 'Ồ', 'Ổ', 'Ỗ', 'Ộ', 'Ơ', 'Ớ', 'Ờ', 'Ở', 'Ỡ', 'Ợ', 'Ø', 'Ō', 'Ő', 'Ŏ', 'Ο', 'Ό', 'Ὀ', 'Ὁ', 'Ὂ', 'Ὃ', 'Ὄ', 'Ὅ', 'Ὸ', 'Ό', 'О', 'Ө', 'Ǒ', 'Ǿ', 'Ｏ', 'Ö'],
             'P'    => ['П', 'Π', 'Ｐ'],
             'Q'    => ['Ｑ'],
             'R'    => ['Ř', 'Ŕ', 'Р', 'Ρ', 'Ŗ', 'Ｒ'],
@@ -715,7 +715,7 @@ protected static function charsArray()
             'Sh'   => ['Ш'],
             'Shch' => ['Щ'],
             'Ss'   => ['ẞ'],
-            'Th'   => ['Þ'],
+            'Th'   => ['Þ', 'Θ'],
             'Ts'   => ['Ц'],
             'Ya'   => ['Я'],
             'Yu'   => ['Ю'],