docs: fix erfcx function signature in README

Author: Planeshifter

lib/node_modules/@stdlib/math/base/special/README.md

@@ -266,7 +266,7 @@ var fcns = special;
 -   <span class="signature">[`erf( x )`][@stdlib/math/base/special/erf]</span><span class="delimiter">: </span><span class="description">error function.</span>
 -   <span class="signature">[`erfc( x )`][@stdlib/math/base/special/erfc]</span><span class="delimiter">: </span><span class="description">complementary error function.</span>
 -   <span class="signature">[`erfcinv( x )`][@stdlib/math/base/special/erfcinv]</span><span class="delimiter">: </span><span class="description">inverse complementary error function.</span>
--   <span class="signature">[`erfcx()`][@stdlib/math/base/special/erfcx]</span><span class="delimiter">: </span><span class="description">scaled complementary error function.</span>
+-   <span class="signature">[`erfcx( x )`][@stdlib/math/base/special/erfcx]</span><span class="delimiter">: </span><span class="description">scaled complementary error function.</span>
 -   <span class="signature">[`erfinv( x )`][@stdlib/math/base/special/erfinv]</span><span class="delimiter">: </span><span class="description">inverse error function.</span>
 -   <span class="signature">[`factorial( x )`][@stdlib/math/base/special/factorial]</span><span class="delimiter">: </span><span class="description">factorial function.</span>
 -   <span class="signature">[`factorial2( n )`][@stdlib/math/base/special/factorial2]</span><span class="delimiter">: </span><span class="description">double factorial function.</span>