Fixes #107. No longer excludes samples with p_hat =0

[mamcisaac]

The call to filter(scientist_work == "Doesn't benefit") is filtering out any replicates where there are no "Doesn't benefit"s in the small sample. As a result any replicates with p_hat=0 are filtered out and are not displayed.

This issue is caused by using a small sample size and a true proportion close to 0 (p=.2).

I have replaced this filtering code with the following

group_by(replicate)%>% summarize(p_hat = mean(scientist_work=="Doesn't benefit"))

Fixes #107.