docs: fix spelling errors for amount in retry (#69)

Fixes https://github.com/googleapis/python-api-core/issues/68

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Fixes https://github.com/googleapis/python-api-core/issues/68
diff --git a/google/api_core/retry.py b/google/api_core/retry.py
index 446d43c..ea89062 100644
--- a/google/api_core/retry.py
+++ b/google/api_core/retry.py
@@ -125,9 +125,9 @@
         https://cloud.google.com/storage/docs/exponential-backoff
 
     Args:
-        initial (float): The minimum amout of time to delay. This must
+        initial (float): The minimum amount of time to delay. This must
             be greater than 0.
-        maximum (float): The maximum amout of time to delay.
+        maximum (float): The maximum amount of time to delay.
         multiplier (float): The multiplier applied to the delay.
 
     Yields:
@@ -333,9 +333,9 @@
         """Return a copy of this retry with the given delay options.
 
         Args:
-            initial (float): The minimum amout of time to delay. This must
+            initial (float): The minimum amount of time to delay. This must
                 be greater than 0.
-            maximum (float): The maximum amout of time to delay.
+            maximum (float): The maximum amount of time to delay.
             multiplier (float): The multiplier applied to the delay.
 
         Returns: