386: revise base64url description

.requirements.txt

@@ -3,4 +3,5 @@ python-jsonschema-objects>=0.3,<=0.3.10
 jsonschema==3.2.0
 ipython
 pyyaml
-ga4gh.gks.metaschema>=0.1.1
+ga4gh.gks.metaschema>=0.1.1
+sphinx ~= 3.5

docs/source/impl-guide/computed_identifiers.rst

@@ -193,7 +193,7 @@ Truncated Digest (sha512t24u)
 The sha512t24u truncated digest algorithm [Hart2020]_ computes an ASCII digest
 from binary data.  The method uses two well-established standard
 algorithms, the `SHA-512`_ hash function, which generates a binary
-digest from binary data, and `Base64`_ URL encoding, which encodes
+digest from binary data, and a URL-safe variant of `Base64`_ encoding, which encodes
 binary data using printable characters.
 
 Computing the sha512t24u truncated digest for binary data consists of

docs/source/requirements.txt

@@ -1 +1,2 @@
-sphinx ~= 3.5
+sphinx ~= 3.5
+jinja2 == 3.0.3