text: Title: Avoid showing histograms for low cardinality quantitative attributes
  Body: There is a bug related to quantitative attributes that have low cardinality. For example, we create a column of values where all the values are `4.0`. There is a warning message resulting from a divide-by-zero error and a histogram that looks, since the range of the computed min/max field is zero. This issue will be resolved if we avoid computing histograms for quantitative values that have low cardinality.
  
  ```
  import pandas as pd
  import lux
  df = pd.read_csv("../../lux/data/car.csv")
  df["Year"] = pd.to_datetime(df["Year"], format='%Y') # change pandas dtype for the column "Year" to datetype
  df["Units"] = 4.0
  df
  ```
  
  ![image](https://user-images.githubusercontent.com/5554675/93612168-c11c7380-fa01-11ea-9253-d03b4f192168.png)
  
  