title: mdy {lubridate} unable to identify "January"
body: <p>I am working with a list of birth dates in the format "January131973". To get the dates from this string, I am using <code>mdy</code> function from <code>lubridate</code> library. Strangely the code was returning NA only for dates in January, but working fine for other months, as below</p>
  
  <pre><code>&gt; mdy("January131973")
  [1] NA
  Warning message:
  All formats failed to parse. No formats found. 
  &gt; mdy("April241973")
  [1] "1973-04-24"
  </code></pre>
  
  <p>The data spans across all months and dates, and years ranging from 1971 to 1990. But the error occurs only for dates in January. I have worked around the input string to get "13January1973" and proceeded with <code>dmy</code> function instead, which has resolved the issue at hand. (<code>ymd</code> also works perfectly fine.)</p>
  
  <p>However, if it can be verified that I am not overlooking any underlying conflicts etc, it will be helpful the next times, and can also help identify unseen issues elsewhere.</p>
  
  <p>Here is a test code I have tried out to check different combinations</p>
  
  <pre><code>library(tidyr)
  library(lubridate)
  x &lt;- data.frame(mmm=month.name, dd=c(15:26), yyyy=c(1973:1984))
  x_mdy &lt;- unite(x, test, mmm,dd,yyyy, sep = "",remove = FALSE)
  lapply(x_mdy$test, mdy)
  x_dmy &lt;- unite(x, test, dd,mmm,yyyy, sep = "", remove = FALSE)
  lapply(x_dmy$test, dmy)
  x_ymd &lt;- unite(x, test, yyyy,mmm,dd, sep = "", remove = FALSE)
  lapply(x_ymd$test, ymd)
  </code></pre>
  
  <p>After running the above code, I have faced the issue only while using <code>mdy</code> with "January". Also note that abbreviated form of the month name also gives the same error (<code>mmm=month.abb</code> in the above df creation.)</p>
  
  <p>Any clarification of this behavior appreciated.</p>