fix alpha checking

docs/Parameters.rst

@@ -677,7 +677,7 @@ Objective Parameters
 
    -  might be useful in case of large-range labels
 
--  ``alpha``, default = ``0.9``, type = double, constraints: ``0.0 < alpha < 1.0``
+-  ``alpha``, default = ``0.9``, type = double, constraints: ``alpha > 0.0``
 
    -  used only in ``huber`` and ``quantile`` ``regression`` applications
 

include/LightGBM/config.h

@@ -615,7 +615,6 @@ public:
   bool reg_sqrt = false;
 
   // check = >0.0
-  // check = <1.0
   // desc = used only in ``huber`` and ``quantile`` ``regression`` applications
   // desc = parameter for `Huber loss <https://en.wikipedia.org/wiki/Huber_loss>`__ and `Quantile regression <https://en.wikipedia.org/wiki/Quantile_regression>`__
   double alpha = 0.9;

src/io/config_auto.cpp

@@ -446,7 +446,6 @@ void Config::GetMembersFromString(const std::unordered_map<std::string, std::str
 
   GetDouble(params, "alpha", &alpha);
   CHECK(alpha >0.0);
-  CHECK(alpha <1.0);
 
   GetDouble(params, "fair_c", &fair_c);
   CHECK(fair_c >0.0);