Upgrade to Pex 2.1.37. (pantsbuild#11826)

This pulls in a fix for `--pex-repository` that will be used to
complete work on pantsbuild#11105.

3rdparty/python/constraints.txt

@@ -1,8 +1,8 @@
-# Generated by build-support/bin/generate_lockfile.sh on Tue Mar 30 10:05:02 AM PDT 2021
+# Generated by build-support/bin/generate_lockfile.sh on Wed Mar 31 07:41:28 PM PDT 2021
 ansicolors==1.1.8
 attrs==20.3.0
 beautifulsoup4==4.6.3
-bugout==0.1.9
+bugout==0.1.10
 certifi==2020.12.5
 cffi==1.14.5
 chardet==4.0.0
@@ -16,7 +16,7 @@ monotonic==1.5
 mypy==0.800
 mypy-extensions==0.4.3
 packaging==20.9
-pex==2.1.36
+pex==2.1.37
 pip==20.2.3
 pluggy==0.13.1
 psutil==5.7.0

3rdparty/python/requirements.txt

@@ -19,7 +19,7 @@ mypy==0.800
 
 packaging==20.9
 pathspec==0.8.0
-pex==2.1.36
+pex==2.1.37
 psutil==5.7.0
 pystache==0.5.4
 # This should be kept in sync with `pytest.py`.

src/python/pants/backend/python/util_rules/pex_cli.py

@@ -37,7 +37,7 @@ class PexBinary(TemplatedExternalTool):
     name = "pex"
     help = "The PEX (Python EXecutable) tool (https://github.com/pantsbuild/pex)."
 
-    default_version = "v2.1.36"
+    default_version = "v2.1.37"
     default_url_template = "https://github.com/pantsbuild/pex/releases/download/{version}/pex"
 
     @classproperty
@@ -47,8 +47,8 @@ def default_known_versions(cls):
                 (
                     cls.default_version,
                     plat,
-                    "b93c015325c3d4cfa0c4e6b8ec8967edeb5fdac909adc8f6cb09b09c14055d93",
-                    "3603974",
+                    "21b5e7c8a0aa5e5315e5253464e8a6c63ecc73938f1192500e0faaa14e81317e",
+                    "3606172",
                 )
             )
             for plat in ["darwin", "linux"]