Update repositories.txt (#6334)

add https://github.com/adafruit/Adafruit_STSPIN

Author: ladyada

repositories.txt

@@ -659,6 +659,7 @@ https://github.com/adafruit/Adafruit_SSD1306
 https://github.com/adafruit/Adafruit_SSD1325_Library
 https://github.com/adafruit/Adafruit_SSD1327
 https://github.com/adafruit/Adafruit_STMPE610
+https://github.com/adafruit/Adafruit_STSPIN
 https://github.com/adafruit/Adafruit_TCA8418
 https://github.com/adafruit/Adafruit_TCS34725
 https://github.com/adafruit/Adafruit_TestBed