support singularity-ce (#1547)

Fixes #1545

Author: mr-c

cwltool/singularity.py

@@ -31,6 +31,8 @@ def get_version() -> str:
         ).strip()
         if _SINGULARITY_VERSION.startswith("singularity version "):
             _SINGULARITY_VERSION = _SINGULARITY_VERSION[20:]
+        if _SINGULARITY_VERSION.startswith("singularity-ce version "):
+            _SINGULARITY_VERSION = _SINGULARITY_VERSION[23:]
         _logger.debug(f"Singularity version: {_SINGULARITY_VERSION}.")
     return _SINGULARITY_VERSION