title: c("region", "value") %in% colnames(user.df) are not all TRUE
body: <p>I'm getting "c("region", "value") %in% colnames(user.df) are not all TRUE" error while creating a choropleth of US ZIP codes using <a href="https://github.com/arilamstein/choroplethrZip" rel="nofollow noreferrer">choroplethrZip</a> package. </p>
  
  <p>I am trying to plot the zip codes of the US map based on the label value in that zip code, using the above packages. I am trying to use the following code but doesn't work</p>
  
  <pre><code>#install.packages("devtools")
  library(devtools)
  
  #install_github("choroplethr", "trulia")
  library(choroplethr)
  
  #install_github('arilamstein/choroplethrZip@v1.5.0')
  library(choroplethrZip)
  
  temp &lt;- read.table("data.txt")
  zip_choropleth(temp)
  </code></pre>
  
  <p>data.txt looks like</p>
  
  <pre><code>region  value
  00601   15
  00602   42
  00603   97
  00604   3
  .       .
  .       .
  </code></pre>