update Sources enum

* linting fix (invalid-name)
* use Sources enum instead of string

app/routers/v2.py

@@ -14,13 +14,13 @@ class Sources(str, enum.Enum):
     A source available for retrieving data.
     """
 
-    jhu = "jhu"
-    csbs = "csbs"
-    nyt = "nyt"
+    JHU = "jhu"
+    CSBS = "csbs"
+    NYT = "nyt"
 
 
 @V2.get("/latest", response_model=LatestResponse)
-async def get_latest(request: Request, source: Sources = "jhu"):  # pylint: disable=unused-argument
+async def get_latest(request: Request, source: Sources = Sources.JHU):  # pylint: disable=unused-argument
     """
     Getting latest amount of total confirmed cases, deaths, and recoveries.
     """
@@ -91,7 +91,7 @@ async def get_locations(
 # pylint: disable=invalid-name
 @V2.get("/locations/{id}", response_model=LocationResponse)
 async def get_location_by_id(
-    request: Request, id: int, source: Sources = "jhu", timelines: bool = True
+    request: Request, id: int, source: Sources = Sources.JHU, timelines: bool = True
 ):
     """
     Getting specific location by id.