[misc] Version bump: v0.8.3->v0.8.4 (#3295)

Author: yolo2themoon

setup.py

@@ -37,7 +37,7 @@
 project_name = os.getenv('PROJECT_NAME', 'taichi')
 TI_VERSION_MAJOR = 0
 TI_VERSION_MINOR = 8
-TI_VERSION_PATCH = 3
+TI_VERSION_PATCH = 4
 version = f'{TI_VERSION_MAJOR}.{TI_VERSION_MINOR}.{TI_VERSION_PATCH}'
 
 data_files = glob.glob('python/lib/*')