webp-container-spec,cosmetics: normalize range syntax
this makes the syntax in this document consistent with
webp-lossless-bitstream-spec.txt
[N-M] -> [N..M]
@@ -589,8 +589,8 @@ where `clip(v)` is equal to:
* v otherwise
The final value is derived by adding the decompressed value `X` to the
-predictor and using modulo-256 arithmetic to wrap the \[256-511\] range
-into the \[0-255\] one:
+predictor and using modulo-256 arithmetic to wrap the \[256..511\] range
+into the \[0..255\] one:
`alpha = (predictor + X) % 256`
