dplyr rename error: contains unknown variables : <p>Very simple, renaming colnames with dplyr gives me an odd error.</p>

<pre><code> library(dplyr)

 df &lt;- data.frame(var1=c("one","two","three"),var2=c(1,2,3)) 

 df &lt;- 
    df %&gt;% 
    rename(var1=are.letters, var2=are.numbers)

Error: `are.letters`, `are.numbers` contains unknown variables
</code></pre>

<p>second try </p>

<pre><code> df &lt;- rename(df, var1=are.letters, var2=are.numbers)

Error: `are.letters`, `are.numbers` contains unknown variables
</code></pre>

<p>Wondering if quoting....</p>

<pre><code>df &lt;- 
    df %&gt;% 
    rename('var1'='are.letters', 'var2'='are.numbers')

Error: `are.letters`, `are.numbers` contains unknown variables
</code></pre>
