Fix typos (#498)

Author: gregorybchris

econml/sklearn_extensions/linear_model.py

@@ -1783,7 +1783,7 @@ def fit(self, X, y, sample_weight=None, freq_weight=None, sample_var=None):
         param, _, rank, _ = np.linalg.lstsq(WX, wy, rcond=None)
 
         if rank < param.shape[0]:
-            warnings.warn("Co-variance matrix is undertermined. Inference will be invalid!")
+            warnings.warn("Co-variance matrix is underdetermined. Inference will be invalid!")
 
         sigma_inv = np.linalg.pinv(np.matmul(WX.T, WX))
         self._param = param

econml/solutions/causal_analysis/_causal_analysis.py

@@ -598,7 +598,7 @@ def fit(self, X, y, warm_start=False):
             f"but was given {self.nuisance_models}")
 
         assert self.heterogeneity_model in ['linear', 'forest'], (
-            "The only supported heterogeneity models are 'linear' and, 'forest but received "
+            "The only supported heterogeneity models are 'linear' and 'forest' but received "
             f"{self.heterogeneity_model}")
 
         assert np.ndim(X) == 2, f"X must be a 2-dimensional array, but here had shape {np.shape(X)}"