Update decimal_to_binary.py (TheAlgorithms#2185)

"an Integer" instead of "a Integer"

Author: Hardik Aggarwal

conversions/decimal_to_binary.py

@@ -4,7 +4,7 @@
 def decimal_to_binary(num: int) -> str:
 
     """
-        Convert a Integer Decimal Number to a Binary Number as str.
+        Convert an Integer Decimal Number to a Binary Number as str.
         >>> decimal_to_binary(0)
         '0b0'
         >>> decimal_to_binary(2)