title: Installation issues of causalimpact in R
body: <p>I followed this instruction from google website about installing causalimpact:</p>
  
  <pre><code>install.packages("devtools")*
  
  library(devtools)
  
  devtools::install_github("google/CausalImpact")
  </code></pre>
  
  <p><em>These codes however gives the following error:</em></p>
  
  <blockquote>
    <p>Warning: package 'xts' was built under R version 3.2.5</p>
    
    <p>Error in loadNamespace(j &lt;- i[[1L]], c(lib.loc, .libPaths()),
    versionCheck = vI[[j]]) :    there is no package called 'Rcpp'</p>
    
    <p>ERROR: lazy loading failed for package 'CausalImpact'</p>
    
    <p>removing
    'C:/Users/grace/Documents/R/R-3.2.4revised/library/CausalImpact'</p>
    
    <p>Error: Command failed (1)**</p>
  </blockquote>
  
  <p>Has anyone encountered this problem and can you give the solution?</p>