fix: minor typo in context_precision.md

[AbhishekRP2002]

for Context Precision without reference definition, i.e LLMContextPrecisionWithoutReference metric can be used when you have both retrieved contexts and also reference contexts associated with a user_input.

Here, it should be reference answer instead of reference contexts as per my understanding

Similarly,

for Context Precision with reference definition i.e LLMContextPrecisionWithReference metric is can be used when you have both retrieved contexts and also reference answer associated with a user_input.

here, reference answer should be replaced with reference context