Omit lines that use pandoc 2.0's markdown divs

[andrewheiss]

Nowadays pandoc includes extra metadata to delineate divs in bibliographies. It used to use HTML like <div>, but now it uses :::. For instance, after exporting two entries with pandoc -t markdown-citations --wrap=none, this is the resulting output:

(Blackwell and Glynn 2018; Cinelli and Hazlett 2020)

::: {#refs .references .hanging-indent}
::: {#ref-BlackwellGlynn:2018}
Blackwell, Matthew, and Adam N. Glynn. 2018. "How to Make Causal Inferences with Time-Series Cross-Sectional Data Under Selection on Observables." *American Political Science Review* 112 (4): 1067--82. <https://doi.org/10.1017/s0003055418000357>.
:::

::: {#ref-CinelliHazlett:2020}
Cinelli, Carlos, and Chad Hazlett. 2020. "Making Sense of Sensitivity: Extending Omitted Variable Bias." *Journal of the Royal Statistical Society: Series B (Statistical Methodology)* 82 (1): 39--67. <https://doi.org/10.1111/rssb.12348>.
:::
:::

The tail -n+5 part of the pandoc command in exportMarkdownReferences.sh takes care of the first few lines with the parenthetical citations, but the old grep -v "</div>" part of the command doesn't do anything anymore and the resulting Markdown text includes all the lines that start with :::.

This change to the pandoc command omits all lines that start with :::, resulting in this output:

Blackwell, Matthew, and Adam N. Glynn. 2018. "How to Make Causal Inferences with Time-Series Cross-Sectional Data Under Selection on Observables." *American Political Science Review* 112 (4): 1067--82. <https://doi.org/10.1017/s0003055418000357>.

Cinelli, Carlos, and Chad Hazlett. 2020. "Making Sense of Sensitivity: Extending Omitted Variable Bias." *Journal of the Royal Statistical Society: Series B (Statistical Methodology)* 82 (1): 39--67. <https://doi.org/10.1111/rssb.12348>.