docs/spec/manifest-v2-2.md: fix ARM variant
The correct `vairant` string for ARM v6 is "v6", not "armv6l".
There is no known implementation that actually uses "armv6l".
See the discussion in opencontainers/image-spec PR 817
@@ -107,7 +107,7 @@ image manifest based on the Content-Type returned in the HTTP response.
- **`variant`** *string*
The optional variant field specifies a variant of the CPU, for
- example `armv6l` to specify a particular CPU variant of the ARM CPU.
+ example `v6` to specify a particular CPU variant of the ARM CPU.
- **`features`** *array*
