docs: Fix spec references in docs

Signed-off-by: Jon Skeet <[email protected]>

Author: jskeet

docs/bindings.md

@@ -1,6 +1,6 @@
 # Implementing a protocol binding
 
-From the [specification](https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#protocol-binding):
+From the [specification](https://github.com/cloudevents/spec/blob/main/cloudevents/spec.md#protocol-binding):
 
 > A protocol binding describes how events are sent and received over a given protocol.
 

docs/formatters.md

@@ -2,7 +2,7 @@
 
 The `CloudEventFormatter` abstract type in the C# SDK is an
 augmentation of the [Event
-Format](https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#event-format)
+Format](https://github.com/cloudevents/spec/blob/main/cloudevents/spec.md#event-format)
 concept in the specification.
 
 Strictly speaking, CloudEvent data is simply a sequence of bytes. In

docs/guide.md

@@ -47,7 +47,7 @@ There are three kinds of attributes:
 - Extension: these attributes are not formalized as part of the
   CloudEvents specification. The CloudEvents specification repository
   [includes descriptions of some extension
-  attributes](https://github.com/cloudevents/spec/tree/v1.0.1/extensions)
+  attributes](https://github.com/cloudevents/spec/tree/main/cloudevents/extensions)
   that may become standardized over time, but they are not
   considered part of the specification.