Update ta-lib wheels

build_helpers/install_windows.ps1

@@ -6,10 +6,13 @@ python -m pip install --upgrade pip
 $pyv = python -c "import sys; print(f'{sys.version_info.major}.{sys.version_info.minor}')"
 
 if ($pyv -eq '3.7') {
-    pip install build_helpers\TA_Lib-0.4.20-cp37-cp37m-win_amd64.whl
+    pip install build_helpers\TA_Lib-0.4.21-cp37-cp37m-win_amd64.whl
 }
 if ($pyv -eq '3.8') {
-    pip install build_helpers\TA_Lib-0.4.20-cp38-cp38-win_amd64.whl
+    pip install build_helpers\TA_Lib-0.4.21-cp38-cp38-win_amd64.whl
+}
+if ($pyv -eq '3.9') {
+    pip install build_helpers\TA_Lib-0.4.21-cp39-cp39-win_amd64.whl
 }
 
 pip install -r requirements-dev.txt