Fix best_f in docs (#277)

Summary:
This was part of 5d8c9a4 but never made it into a PR.
Pull Request resolved: #277

Reviewed By: sdaulton

Differential Revision: D17564747

Pulled By: Balandat

fbshipit-source-id: e8a9c36c4939b92af2cf342846efc4a80bbfa845

Author: Balandat

botorch/acquisition/monte_carlo.py

@@ -112,8 +112,7 @@ def __init__(
 
         Args:
             model: A fitted model.
-            best_f: The best (feasible) function value observed so far (assumed
-                noiseless).
+            best_f: The best objective value observed so far (assumed noiseless).
             sampler: The sampler used to draw base samples. Defaults to
                 `SobolQMCNormalSampler(num_samples=500, collapse_batch_dims=True)`
             objective: The MCAcquisitionObjective under which the samples are
@@ -254,8 +253,7 @@ def __init__(
 
         Args:
             model: A fitted model.
-            best_f: The best (feasible) function value observed so far (assumed
-                noiseless).
+            best_f: The best objective value observed so far (assumed noiseless).
             sampler: The sampler used to draw base samples. Defaults to
                 `SobolQMCNormalSampler(num_samples=500, collapse_batch_dims=True)`
             objective: The MCAcquisitionObjective under which the samples are