Fix type in __init__.py -> `. " (#1250)

It can be installed with `conda install -n base -c conda-forge mamba`. "

snakemake/__init__.py

@@ -2557,7 +2557,7 @@ def parse_cores(cores):
                 "The mamba package manager (https://github.com/mamba-org/mamba) is an "
                 "extremely fast and robust conda replacement. "
                 "It is the recommended way of using Snakemake's conda integration. "
-                "It can be installed with `conda install -n base -c conda-forge mamba."
+                "It can be installed with `conda install -n base -c conda-forge mamba`. "
                 "If you still prefer to use conda, you can enforce that by setting "
                 "`--conda-frontend conda`.",
                 file=sys.stderr,