> biocLite("BiocParallel")
BioC_mirror: https://bioconductor.org
Using Bioconductor 3.8 (BiocInstaller 1.31.1), R 3.5.0 (2018-04-23).
Installing package(s) ‘BiocParallel’
Warning message:
package ‘BiocParallel’ is not available (for R version 3.5.0) 
> sessionInfo()
R version 3.5.0 (2018-04-23)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.4 LTS

Matrix products: default
BLAS: /usr/lib/libblas/libblas.so.3.6.0
LAPACK: /usr/lib/lapack/liblapack.so.3.6.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] BiocInstaller_1.31.1

loaded via a namespace (and not attached):
[1] compiler_3.5.0 tools_3.5.0   

The 'devel' software repository was 'flushed' (all packages removed then repopulated) so that packages would include a Date/Published: field inserted by the nightly builder. Unfortunately, package that fail to build do not get pushed to the flushed repository, and BiocParallel had a timeout on the nightly builds. Until the timeout clears, your best bet is to install this from source

git clone https://git.bioconductor.org/packages/BiocParallel
R CMD INSTALL BIocParallel

This problem is transient, and only a small number of packages are affected.