Add singularity 3.5.2 version

Signed-off-by: Geoffroy Vallee <geoffroy.vallee@gmail.com>

Author: gvallee

etc/sympi_singularity.conf

@@ -13,3 +13,4 @@ master=https://github.com/sylabs/singularity.git
 3.4.2=https://github.com/sylabs/singularity/releases/download/v3.4.2/singularity-3.4.2.tar.gz
 3.5.0=https://github.com/sylabs/singularity/releases/download/v3.5.0/singularity-3.5.0.tar.gz
 3.5.1=https://github.com/sylabs/singularity/releases/download/v3.5.1/singularity-3.5.1.tar.gz
+3.5.2=https://github.com/sylabs/singularity/releases/download/v3.5.2/singularity-3.5.2.tar.gz