chore: bump version to 0.3.15

Author: xmatthias

setup.py

@@ -19,7 +19,7 @@
         "pandas_ta.volatility",
         "pandas_ta.volume",
     ],
-    version=".".join(("0", "3", "14b")),
+    version=".".join(("0", "3", "15")),
     description=long_description,
     long_description=long_description,
     author="Kevin Johnson, the Freqtrade Team",