Rephrase

Signed-off-by: Thomas Poignant <[email protected]>

specification/sections/03-evaluation-context.md

@@ -36,7 +36,7 @@ see: [structure](../types.md#structure), [datetime](../types.md#datetime)
 
 > The evaluation context fields **MUST** have an unique key.
 
- The key uniquely identifies any the field in the `evaluation context` and it should be unique accross all types to avoid any collision when marshelling the `evaluation context` by the provider.
+ The key uniquely identifies a field in the `evaluation context` and it should be unique accross all types to avoid any collision when marshelling the `evaluation context` by the provider.
 
 ### Merging Context