Travis ci build failed due to installed package but not found

The Travis CI build of a github pull request I did fails after trying to load a the package mgcv. I get in the ‘Checking package’ section:

Error: processing vignette … failed with diagnostics:
there is no package called ‘mgcv’
Execution halted

However, this package appears above in the section ‘Installed package versions’:
package *version date lib source
mgcv 1.8-26 2018-11-21 [2] CRAN (R 3.5.2)

Also, I have installed the same versions of R and of that package in my computer, and I have no problem to run the same file.

Please provide a link to the failing build.

The link:

Could it be a problem due to the package parallel is not installed?