Properly sort versions in "emsdk list" (#508)

Split version to integers but avoid exceptions in case there is a
non-numerical character in some version.

Comparison:
    Before   |   After
    1.39.9       1.39.16
    1.39.8       1.39.15
    1.39.7       1.39.14
    1.39.6       1.39.13
    1.39.5       1.39.12
    1.39.4       1.39.11
    1.39.3       1.39.10
    1.39.2       1.39.9
    1.39.16      1.39.8
    1.39.15      1.39.7
    1.39.14      1.39.6
    1.39.13      1.39.5
    1.39.12      1.39.4
    1.39.11      1.39.3
    1.39.10      1.39.2
    1.39.1       1.39.1
    1.39.0       1.39.0
    1.38.48      1.38.48
    1.38.47      1.38.47
    1.38.46      1.38.46
    1.38.45      1.38.45
    1.38.44      1.38.44
    1.38.43      1.38.43
    1.38.42      1.38.42
    1.38.41      1.38.41
    1.38.40      1.38.40
    1.38.39      1.38.39
    1.38.38      1.38.38
    1.38.37      1.38.37
    1.38.36      1.38.36
    1.38.35      1.38.35
    1.38.34      1.38.34
    1.38.33      1.38.33

emsdk.py

@@ -2918,8 +2918,11 @@ def main():
       print('')
 
     print('All recent (non-legacy) installable versions are:')
-    releases_versions = sorted(load_releases_versions())
-    releases_versions.reverse()
+    releases_versions = sorted(
+      load_releases_versions(),
+      key=lambda x: [int(v) if v.isdigit() else -1 for v in x.split('.')],
+      reverse=True,
+    )
     for ver in releases_versions:
       print('         %s    %s' % (ver, installed_sdk_text('sdk-releases-upstream-%s-64bit' % get_release_hash(ver, releases_info))))
     print()