Update version of nbformat used

In more recent versions of Python like 3.10, the `base64` package
changed APIs, and this in turn caused nbformat 4.4.0 to fail to work.
Updating to the latest version (5.1.3) solved that problem.

A minor tweak was also needed in scripts/format_ipynb.py to account
for a different error class being returned when "!pip ..." commands
are encountered in the notebook file.

Author: mhucka

requirements.txt

@@ -2,7 +2,7 @@ cirq-core==1.3.0
 cirq-google==1.3.0
 sympy==1.12
 numpy==1.24.2  # TensorFlow can detect if it was built against other versions.
-nbformat==4.4.0
+nbformat==5.1.3
 pylint==2.4.4
 yapf==0.40.2
 tensorflow==2.15.0

scripts/format_ipynb.py

@@ -30,7 +30,7 @@
         try:
             fmt_lines = yapf.yapf_api.FormatCode(''.join(lines),
                                                  style_config="google")[0]
-        except SyntaxError:
+        except (SyntaxError, yapf.yapflib.errors.YapfError):
             continue
         # google style always adds an EOF newline; undo this.
         all_cells[i]['source'] = fmt_lines[:-1]