docs: fix grammar (#727)

Author: ralme1da

packages/core/stellar/README.md

@@ -38,12 +38,12 @@ Import the contract type(s) (for example, `fungible`) that you want to use from
 import { fungible } from '@openzeppelin/wizard-stellar';
 ```
 
-To generate the source code for an Fungible contract with all of the default settings:
+To generate the source code for a Fungible contract with all of the default settings:
 ```js
 const contract = fungible.print();
 ```
 
-To generate the source code for an Fungible contract with some custom settings:
+To generate the source code for a Fungible contract with some custom settings:
 ```js
 const contract = fungible.print({
   pausable: true,

packages/core/stellar/src/fungible.ts

@@ -204,7 +204,7 @@ function addPremint(c: ContractBuilder, amount: string) {
 }
 
 /**
- * Calculates the initial supply that would be used in an Fungible contract based on a given premint amount and number of decimals.
+ * Calculates the initial supply that would be used in a Fungible contract based on a given premint amount and number of decimals.
  *
  * @param premint Premint amount in token units, may be fractional
  * @param decimals The number of decimals in the token