Fix "play build-module" by replacing yaml.load with yaml.safe_load

This fixes an error when "play build-module" is run on Python 3.7.11:
  load() missing 1 required positional argument: 'Loader'

This follows the recommendation shown on
  https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load(input)-Deprecation

A loader argument is now required.  This commit assumes that
dependencies.yml uses standard YAML tags, and so uses safe_loader.
This is the most secure loader.

framework/pym/play/commands/modulesrepo.py

@@ -328,7 +328,7 @@ def build(app, args, env):
     if os.path.exists(deps_file):
         f = open(deps_file)
         try:
-            deps = yaml.load(f.read())
+            deps = yaml.safe_load(f.read())
             if 'self' in deps:
                splitted = deps["self"].split(" -> ")
                if len(splitted) == 2:
@@ -354,7 +354,7 @@ def build(app, args, env):
 
     if os.path.exists(deps_file):
         f = open(deps_file)
-        deps = yaml.load(f.read())
+        deps = yaml.safe_load(f.read())
         if 'self' in deps:
            splitted = deps["self"].split(" -> ")
            f.close()