[NODE][Serialization]fix serialization precision loss in float (#4503)
[NODE][Serialization]fix serialization precision loss in float (#4503)

* fix serialization precision loss in float

When we want to serialize a tvm.tensor object(like pickle)， we will get a precision loss cause by std::to_string()。
For example, a2.value will be 0.0 while a.value=0.00000001 in the following: 
    import tvm
    import pickle
    a = tvm.const(0.00000001, 'float32')
    a2 = pickle.loads(pickle.dumps(a))

* remove line end spaces

tqchen/tvm,Laurawly/tvm-1,dmlc/tvm,sxjscience/tvm,dmlc/tvm,dmlc/tvm,tqchen/tvm,tqchen/tvm,Laurawly/tvm-1,sxjscience/tvm,Laurawly/tvm-1,tqchen/tvm,dmlc/tvm,Laurawly/tvm-1,tqchen/tvm,sxjscience/tvm,sxjscience/tvm,sxjscience/tvm,Laurawly/tvm-1,dmlc/tvm,tqchen/tvm,tqchen/tvm,Laurawly/tvm-1,dmlc/tvm,Laurawly/tvm-1,dmlc/tvm,dmlc/tvm,sxjscience/tvm,tqchen/tvm,sxjscience/tvm,tqchen/tvm,dmlc/tvm,Laurawly/tvm-1,sxjscience/tvm,sxjscience/tvm,Laurawly/tvm-1,Laurawly/tvm-1,tqchen/tvm